No design is going to accommodate all shooters. My understanding was that Smith went to round butts on larger frames in order to standardize and reduce costs, not because of ergonomic reasons.
Actually, there are very, very few options for conversion grips, and most of them don't really add any girth to the grip. I'm having Mr. Culina make a set for me now because of that problem. Slimmed down square butt grips are easier to find by a long shot that fattened up conversion grips.The Ahrends conversion grips were no better than the Hogue that came with my 686.