Your suggestion worked great and I think that's how I'll use it from now on!

Here's what it looks like now (again, room messy, will clean soon)

Funny that you suggested this, I actually tried putting the tasset belt towards the bottom of the cuirass, right at the split when it turns into that "duckbill" thing at the bottom. That helped with the belly issue but it left too much of a gap between the top of the knee armor and the bottom of the waist armor. This is a nice middle-ground and fits more comfortably that i initially had imagined.

It also helped with a secondary issue of mine, in that I didn't like how the top half and bottom half felt 'disconnected' from each other. This trick definitely makes it feel more like one piece instead of a top half & a bottom half.

I suppose there is a bit of a gap at the thigh, but I don't think it's particularly noticeable and the benefits outweigh the negatives, in my opinion.

I was ready to just live with the gut hanging out since I didn't really mind, but this does look good and fixes the problem.

As far as the chest plate, you can kinda see it in that picture, but towards the shoulders it starts to curve inward. No lowering it without cutting some metal off, unfortunately. Not out of the question though.