I think ID is severely slowed down by low SB. I don't know if RB relies on SB though, but I always thought SB is the "glue" that speeds up or slows down both ID and RB, same as HA speeds up or slows down PA and OD. However, I don't think slowing of ID because of low SB is really noticable, because inside skills train so fast on tall players. Also more and more tall players train at least a bit of OD which trains also ID.