Info needed: 13 cab windshield question

[Bruce Parker (RIP)]

Regarding the front outer windshield posts on 13 cab CMP Chevs (not sure about Fords), it seems the left and right sheet metal skin with the 'press the dot' fasteners for the side curtain canvas are different. The left is rectangular and the side surface is flat, whereas the right often has a gentle bulge. So my question is, should the bulge be there, and if so, why? Or is it not supposed to be there and for some reason the rust bulge (because what else could it be) only affects the one side because of some flaw perhaps?

I need to know as replacing these post skins is on by to-do list.

Here's what I mean. This is a little bump but some are quite rounded.