Many Jacket type (wrap around) BDC’s have this problem. Some manufacturers have attempted to compensate for this problen by using elastic waist bands, etc...
I dive with back plate and wings when I’m diving for fun, exploration, etc. but I use a Jacket Type BCD when I’m with Basic Open Water students. Here is what I’ve found through the years:
1) Make sure that you have the proper size BCD and that it is adjusted properly.
2) Make sure that you are properly weighted. If you must inflate the BCD completely in order to stay on the surface, then it is quite possible that you are wearing too much weight. The more air you put into the BCD, the more it expands, and the more it squeezes you...
3) Having taken care of the first two issues... select a BCD that is engineered to compensate for the "squeeze" effect. one that you are comfortable with, and then stick with it.
Just some suggestions...
Ron sends