Not quite sure I understand the question, but here's a little tidbit that I do know... maybe it will help?
The small frame size S&W is the j-frame. I have a model 60, 5-shot J-frame and it's slightly smaller with a slightly smaller cylinder than an SP-101. When I tried to fit a .327 Fed Mag SP-101 in to my DeSantis leather holsters built for the J-frame S&W, it was too tight a fit. Could be wedged in there, but clearly was too small.
The S&W K-frame is one frame size up from the J-frame, and would likely be a tiny bit larger than an SP-101.