Hi Overthinker,
I forgot to reply to this in my last reply. the salesperson is correct so if you have a 6" layer of material that is rated at a particular ILD (for latex) or IFD (for polyfoam) then all the thinner layers that are cut from the same layer would be the same ILD. ILD/IFD is tested on a layer that is a “standard” thickness (generally 6" in the case of latex and 4" in the case of polyfoam) and all the layers that are slit from the same core (in the case of latex) or the same foam bun (in the case of polyfoam) would be rated at the same ILD.
If the Qualux is 3.0 lb density then it’s likely to be HR but I would pay much more attention to whether the mattress is a good “match” for you in terms of PPP than I would in trying to find out whether it meets all the technical specifications for HR polyfoam which you are unlikely to be able to find out anyway and won’t make any meaningful difference in the durability of the mattress. What your body tells you when you test the mattress for PPP is much more important than finding out the compression modulus and resilience percentage of the Qualux. Resilience is measured by the percentage rebound when a steel ball is dropped on a material under specified conditions. If the ball (or in most cases a pendulum) that is used for testing bounces back to 60% of the height that it was originally dropped from then it would have a resilience rating of 60%.
You may be making this much more complex than it needs to be.
The first “P” means “Posture and alignment” which is all about whether your testing indicates that your spine and joints are in neutral alignment on the mattress “as a whole” in all your sleeping positions. I would use the testing guidelines in the tutorial post for this.
The second “P” means “Pressure relief” which is all about whether your testing indicates that the mattress “as a whole” relieves all your pressure points in all your sleeping positions. Once again I would use the testing guidelines in the tutorial post to decide this.
The third “P” means “Personal preferences” and also applies to the mattress “as a whole”. Most of these are listed in post #46 here.
This would depend on what you mean by “support” and the specifics of what you are trying to change because these typed of questions generally have many “it depends” in the answer. I would keep in mind that all the layers will have some effect on all the other layers and components both above and below them so you can’t change one of the "P’s without having some effect on the others as well.
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel”.
If you are trying to change the primary support of a mattress because you are sinking down too far into the mattress and waking up with lower back pain or stiffness then this would normally be a matter of either using firmer deeper layers or thinner upper layers (which would put you closer to the firmer deeper layers). The only way to know with any certainty whether any mattress is a good “match”: for you in terms of PPP will be based on your own trial and error and sleeping experience.
This is also in the testing guidelines that are linked in the tutorial post but I would suggest a minimum of 15 minutes as a good guideline.
Phoenix