Hi Betz,
Without getting into the details of how certain layering patterns work together … this is called a “dominating layer” where a firmer layer is over a softer layer.
All the layers interact together and affect each other to different degrees as they compress and the only thing that matters is whether it provides you with the PPP (Posture and alignment, Pressure relief, and personal preferences) you need. There is nothing in any way “wrong” with having a firmer layer over a softer layer depending on the goal . it will provide a little bit firmer sleeping surface with less sinking in on top but will have some softness underneath so that the medium layer wouldn’t feel as firm as having a firmer layer underneath it. This would be the softest version of having a medium layer on top.
You can read a little more about the differences between them in post #7 here but I wouldn’t factor in anything in as far as “theory” goes and I would leave all the assessments to how your body feels on each layer combination and what your body (not your mind) tells you. If you start getting into all the technical differences between them it will only become a distraction. In very general terms … Dunlop will feel a little firmer than the same ILD of Talalay because it’s denser and gets firmer faster than Talalay as you sink into it more but I wouldn’t get involved in the technical “stuff” because your actual experience on each combination is much more important.
Phoenix