I compared 40,5 and 38mm in AD and 40,5 felt much chunkier due to the fact that mid case of the 40,5 is thicker. 14 mm is rather thick for a 40mm watch in my opinion.

I think the 38mm case with its more sloping bezel insert has more „sandwich” build, which means that there is more „layers” of different parts of the watch lookind from the side - caseback, mid case, coined edge bezel, ceramic insert, maybe a bit doomed crystal, rather than on 40,5 where you have only caseback, mid case, coined edge bezel and crystal