Hello SleeplessinDallas,
Your post really has 2 separate “parts” so I will reply in 2 posts to keep them separate. The first of these is the idea of “pushback” itself and what it really is which I will “explore” in this post. The second is about the specific mattresses you are commenting on or asking about which I will reply to in the next reply.
So first of all … about pushback …
What some people describe as pushback is really about some combination of resilience, resistance, shear forces, and pressure distribution along the body.
If for example I carved out a piece of wood that was a perfect replica of your body profile in perfect alignment while you were sleeping on your side, it would spread out the weight of your body and could provide great pressure relief. There would be more of your weight on your hips than on your lumbar but you would not feel this pressure as your hips are “designed” to hold more pressure than your lumbar area.
If I now carved out a thin (say 1/4") slice under your hips … they would sink in more deeply which would in turn shift some of the pressure from your hips to your lumbar as your hips would “pull” your lumbar area down onto the wood. This would decrease the pressure on your hips but increase it on your lumbar (waist) area. If this increased the lumbar pressure to a point where it was uncomfortable for you (greater than your comfort threshold) … it would not be because the wood was “pushing back” but because the wood was “resisting” the change in position and the hips were sinking in too far for your comfort and transferring more pressure to your waist area.
In the same way if you shifted position on to your back … the “perfect” shape while you were on your side would now be “not so good” as the lumbar area (small of your back) is not as recessed on your back as the lumbar area (waist) is on your side so your lumbar would be bearing more weight on your back than on your side. This too would not be “pushback” but because the wood could not adapt to a new position. Your hips would be sinking in too far “relative” to your lumbar in that position and there would be too much “pressure” or “support” under the recessed part of your lumbar spine.
Of course a “wood” mattress is not practical since it would only relieve pressure and keep you in alignment if you were perfectly still in the “perfect” position all night since it does not adjust to changes in a sleeping profile. Even the smallest movement would put pressure on parts of your body unlike a material that can “adjust” to changes.
In the same way, if you were to lay on your side or back “across” a large pipe that was under your waist/lumbar and that had no “support” under your hips or shoulders … them most of your body weight would be supported on your lumbar/waist because your shoulders and hips were not being “held up” and this would be very uncomfortable not because the pipe was “pushing back” but because your hips and/or shoulders were sinking down too far and were not bearing enough weight.
“Pushback” is also a term that some people use to describe the “resilience” or “springiness” of a material … and latex in general is the most resilient of all the foam materials (although springs are more resilient than latex and some types of latex are more resilient than others). Resilience is related to the ability of a material to store and return energy and is measured by the percentage of the rebound when a steel ball is dropped on a material rather than its opposite which is hysteresis which is the ability of a material to absorb energy. Lower resilience and higher hysteresis produces less bounce. A more resilient sleeping surface can also result in higher shear forces (forces that “act” in opposite directions) which some people are sensitive to.
Resilience is something that you can only feel with movement because when your body is at rest on a mattress the compression forces of your body pushing down are balanced by the increasing resistive forces of the mattress (regardless of the resilience of the materials in the mattress) and there is no longer any “direction” to the forces which are in equilibrium.
So in essence … when people describe a feeling of “too much pushback” that they connect to a certain material, can be because of it’s resilience or because their hips or other body parts are sinking in too far and the area of the body where they are feeling too much pressure is holding up too much weight.
The “fix” for the “feeling” that the mattress has too much resilience or shear forces on the sleeping surface can be to use a less resilient or more “relaxed” material with less shear forces as a quilting layer, as the top layer, or as a topper on the mattress (see post #18 here)
The “fix” for issues that are connected to feeling too much pressure in certain parts of the body could be to have a firmer material under the hips (occasionally the shoulders) so they don’t sink in so far and shift the pressure away from parts of the body that are not as comfortable with bearing weight. All materials can lead to this feeling in certain constructions but it is often believed that it is a “function” of latex (which has a higher progressive resistance and higher resilience than other foam materials) rather than a function of a construction or layering that is not suitable for a particular individual.
This feeling of “too much pushback” can be particularly aggravated when people are used to sleeping in multiple positions and have a mattress which accommodates (distributes pressure) in some of their sleeping positions but not others. This can often be “fixed” through changes in thickness or ILD of the comfort layer, by adding a softer topper, or through an increase in firmness under the hips in the support layers. I have seen many people try to “fix” the wrong thing or problem (this is very common in the forum you were referring to) and change the “hardness” or “softness” of the wrong layer which can often aggravate the problem rather than fix it. This in turn leads to the belief that certain materials are “not for me” rather than “certain types of layering” or construction are not for me.
The Westin bed for example would have a thicker very soft foam on top and a much firmer innerspring underneath it. This indicates that the “fix” for a correct latex layering would be to use a much softer layer of latex on top and a firmer layer underneath it. Adjustments in layer thickness can also play a big role in this. This would lead to less pressure on the lumbar/waist area in the “problem” sleeping positions (what people generally call “pushback”).
The Night Therapy would likely have the “opposite” problem … it has a very firm innerspring (12 gauge) with only 1" comfort layer which means that there would likely be too much pressure on your hips (which is the feeling you get that it is “too firm” and uncomfortable) even though it doesn’t have too much pressure in the lumbar area.
The “secret” to mattress construction is to balance weight distribution with spinal alignment using different ILD’s and thickness of layers so that the construction “fits” the unique body profile and pressure tolerances of each individual. Each type of material has different reactive qualities or what is called “progressive resistance” which also need to be taken into account in layering thickness or softness. This is often difficult in people with multiple sleeping positions but certainly in my experience there is almost always a “solution” if the correct “problem” is addressed.
Hope this helps a bit with the understanding of what “pushback” really is and I’ll address the rest of your questions and comments in the next post 
Phoenix