Timing curves

Consider a situation where initial timing is advanced a pretty good bit due to cammage and the setup of mechanical advance to take that into account.

With a 'normal' setup as example, you might have 10ºBTDC set for initial timing with mechanical starting in the low-teens-RPM somewhere...call it 1200rpm. If initial timing is set to 20ºBTDC should the centrifugal be sprung to start at a higher RPM, or should the mechanical curve START be at the same place it was? I don't see how the latter would work.

Granted, 10º will have to be taken out of the distributor to get to the same total timing you started with given the 10º initial change, but that is not my question.

Seems like a reasonable situation to get rid of the secondary 'long loop' spring, to put a secondary spring in with a holding-action early in the RPM sweep. Yes, I understand that would do away with the 'two stage' advance curve....but you're already starting at 20ºBTDC in this example.