I think a combination of the TKO formula, Art Alphin's penetration index and a lower bound kinetic energy threshold is what we're looking for. The TKO takes rewards bullet diameter and momentum, the penetration index penalizes bullet diameter somewhat but rewards SD and momentum, and kinetic energy should act as a minimum threshold. The penetration index and kinetic energy thresholds should eliminate the baseball problem. Since the 375 H&H has long been considered a good cape buffalo and adequate elephant caliber it gives us a starting place:

375 H&H shooting a 300g bullet at 2550 fps: TKO 40 PI 120 KE 4330

416 Rigby shooting a 400g bullet at 2400 fps: TKO 57 PI 124 KE 5115

500 Jeffery shooting a 570g bullet at 2400 fps: TKO 99 PI 112 KE 7288

and just to add to the mix ...

375 Weatherby shooting a 350g bullet at 2550 fps TKO 47 PI 163 KE 5052

I'd love to see the 375 Weatherby Penetration Index validated with some empirical testing.

Just some data to think about, no conclusions on my part.