Distributor starting point for a curve

The FBO plates require a lot of fiddling or the curve is too much at low rpm and then gets cut off too early. With a distributor machine and knowledge its easier to do that (use the plates and then change or adjust springs to get it right ).
Easier for most people looking for more performance not to fiddle with springs etc. The way to do that is to shorten the inside of the slots. That way the only part of the curve cut off is the beginning. Then set the intial like a non-CAP equivalent, or use that chart linked above for a modified engine.

The reason for shortening the beginning is many emission era distributors have fast long advances off-idle to make up for reduced initial timing. Initial timing was reduced starting with CAP to reduce emissions at idle speed. (This is OK when everything is setup 100% stock but not when things get modified.)

Racers used to set timing at mid or high rpm and not worry so much about initial. OK with some distributors but less than ideal; especially with street driven automatic transmission cars.