Not sure about the fold width decreasing towards the front, but there is a good reason for having the fold width increase towards the front. When I built a set of replacement bellows for a half plate mahogany folding camera I picked up cheaply, I wasn't sure if my new bellows would compress enough to fit into the space available when the camera was folded. When I followed the dimensions of the old bellows, with fold width increasing towards the front, I found that the bellows actually folded into itself, and assumed a total thickness that was less than the thickness of the material multiplied by the number of folds.
Clever people those old camera makers!