I hear you on the challenges of casting big fat bullets in bulk.
When I get set up to cast for the sixteen bore rifles, I get everything out and do piles of everything.

Also, on your point-blank theory, I'm sure you'd be fine with one leaf.
I'd be interested to see if you can get a load that nails point of impact at point of aim with each leaf.

In the past I have used a similar approach (sight heights, barrel length, ballistic software...) in attempt to determine what projectile type/shape/weight a rifle had been regulated for. In the end I've gotten close with a few different rifles.
The work on paper with pencil is fun, but it's even more rewarding to get the lead on paper with gunpowder!!

Cheers
Tinker