Sorry for the late reply @csehz, missed this one somehow. The smooth brush often does result in slighting shrinking on convex shapes, but with concave shapes it’s the opposite. Also with an extreme pole in the topology, the smooth brush can create a noticeable pinch instead of shrinking. I think an “average of vertices” is the best description of its function, which can result in shrinking if the conditions are right.
If the size of your sculpture is changing noticeably from the smooth brush, I’d say you’re using it too much or too strongly. Relying too heavily on the smooth brush can be a negative thing.
