Resource Utilzation Report

Maybe. This breaks out Register-Only ALUTs and Combinational-Only ALUTs. In many cases the fitter could merge these into a single ALUT, thereby making your design more dense. If you go into the fitter report and Logic Utilization, there is a line-item called Estimated Pairs Recoverable by Packing Register-Only ALUTs with Combinational(I'm paraphrasing). It's a negative number, and basically the fitter's way of saying, "I think I could pack this much together and improve density if I had to". I've seen cases where this is a very large number.

It's not done on a hierarchical level because, naturally, there is no reason these node from different hierarchies can't be packed together. Also note that as it packs more together, performance can start to decrease, so there is a trade-off. As you start to add more logic, you will see more and more packed together. (There was a time when the fitter report didn't do this, and people found they could fill their devices up to 100%, and then keep adding logic and it would fit. They were happy, but all the people that bought larger parts than they needed probably were not, or designs lost because of this)

Bottom line is that area is not a black-and-white value. This is good in that the fitter has flexibility, it just makes it hard to estimate early on. I would probably take that negative number, and just make it a percentage that is the average reduction, and apply it to the sum value you had above. (There are actually more things to consider than that, as the fitter report's Logic Utilization shows, just not on a hierarchical basis.)