Hi baddog,
Both of these comments were just a way of saying “it depends” on the specific design and combination of materials in a mattress.
For example if you have a thinner comfort layer on top of a support core then you may need a lower ILD support core because you could “go through” the comfort layer and compress the deeper layers below it more and with a thinner comfort layer and a larger differential between the ILD’s you may feel too much of the firmness of the support core below it for you to be comfortable on the mattress.
The ILD of a latex core is measured by the force it takes to compress a 50 sq inch round compressor plate 1.5" into the core so the ILD only measures the firmness at 1.5" of compression on a 6" core. All foam materials become firmer as you sink into them more deeply so it would take more force to compress the foam more deeply than 1.5" (the rate that a foam material becomes firmer with deeper compression is called the compression modulus of the foam) so if you had a thinner comfort layer then you would be compressing the support core more deeply and it would “act” firmer and be more “supportive” than if you had a thicker comfort layer on top of the same support core.
Different types and blends of latex also have a different compression modulus and the ILD of different types and blends of latex may not be directly comparable to each other as well (see post #6 here)
There are also many other “specs” that combine together as part of the design of a mattress that makes one mattress suitable for one person and not another and ILD by itself can be somewhat misleading because it isn’t the only specification that determines the feel and performance of a mattress or how “supportive” a support core may be (see post #2 here).
Unless you have a great deal of knowledge and experience with different types of mattress materials and specs and different layering combinations and how they combine together and can translate them into your own “real life” experience … I would tend to avoid using ILD numbers or other complex specs to try and predict how a mattress will feel for you and focus more on your own actual testing and experience or if you can’t test a mattress in person then a more detailed phone conversation with an online manufacturer or retailer. If you try to become an “expert” in mattress theory and design it could take you years to learn enough to design your own mattress using specs that can be more complex than you may realize and I would focus more on your own testing which “bypasses” the need to know anything about specs at all or alternatively talking to knowledgeable and experienced manufacturers or retailers who already know what you would otherwise need to learn before you would be able to choose a mattress.
Phoenix