Hi Pat,
I wonder if your "sunken areas" mean those dry matte patches that appear at random areas of your paintings? I share the same problem, and i find they are like wild mushrooms, popping up when and where they like it!
But i realized that after the painting's dry, i spray retouch varnish to give it that even sheen...that does solve the problem temporarily for me. And six months' down the road, i'll be able to put up that more permanent varnish on the paintings.