Rich's experiments also show faster ignition with powder banked against the hole - opposite of what 'Ol Sam' writes or has written. Jim may be writing of "our own" Pletch's timing experiments or perhaps others - fact is sometimes opposite of what has been repeated for many years by many writers. As well, 4F IS faster than 3f or 2F. Can 2F or 3f be used? Absolutely, just not as fast as 2F - Swiss NulB is even faster.
I always fill the pan now, with 4F - always, no matter what or whose flinter I am shooting. Yes, it uses more 4F prime and yes more prime causes more fouling on the lock - no matter. I need every advantage I can find when shooting flinters. I also never wipe the frizzen nor flint for an entire day's shooting. Fouling does not build up on the face of the frizzen - the flint seems to keep it quite clean. Some times while shooting you may have a flash in the pan and have to poke the vent open and some times you may have to nap your flint if you have a "fail to fire"- KLATCH!, otherwise I find all of my flinters need very little shot to shot maintenance - load, prime and that's it. It's even better with one of Bill's Locks.