Post 44 shows it and Rob's explains how to figure it in post 48.
Another picture in
lets revisit timing
The reasons push welding the inside are
a) Most of the electronic distributors are from the early smog era. The advance immediately above idle rpm is designed to make up for the retarded initial timing and get back to normal. This part of the advance isn't wanted with a normal inital timing. Even more so with a hot rod engine that wants an initial of 15 degrees or more.
b) Stopping the advance early in the rpms with eletronic ignition results in retard. This was an old 1/4 mile trick that worked fine with points but not with electronics.