Math section
Each body section has its own table because that way is more neat (also according to Putnam clothes in one section don't affect the others even if they cover overlapping body parts).
Note: I'm assuming humanoid body distributions for now. Until I get the body data for all the races this is the best I can do to calculate the size of each armor piece. This should provide accurate results for most normal races like dwarfs, humans and so on.
Note 2: I'm assuming that the size of each armor layer affects the following armor layers (on the same body part). This is an assumption, since I haven't been able to find any information about it. In theory, it could be this way or the size could be independent (in which case the size of every layer except the first one would be smaller than what the tables said).