[Joe K]

Vince Falter (Fordgarage.com) says that the manual adjust "span range" of the Model A distributor timing is about twice what is needed.

If you have to go much above horizontal on the handle, you're probably too advanced - or your initial timing on the Model A engine is off.

Also, the "built in timing" of the Model B engine centrifugal distributor is about half the span of the Model A manual timing span.

I can see that one might narrow the optimal timing band even more with elevated compression. The engine will be more "sensitive" to an off setting.

Joe K