Hi Turtlebed,
Yes this makes sense. Thinner mattresses become firmer faster as you sink into them (see post #14 here about the effect of thickness) and many people find that prefer or do better with an extra 2" or 3" of latex in terms of PPP … particularly if they sleep on their side.
The choice between Dunlop and Talalay in the top layer (or any layer of the mattress) would be a preference choice and would depend on the firmness and “feel” that you prefer (see post #7 here for more about the differences between the “feel” of Dunlop and Talalay). Both are good quality materials.
Phoenix