There is no direct (linear) cross-over, and it's highly cylinder head-specific. The cylinder pressure curves of "high lift short duration" vs. "low lift long duration" will look completely different even with the same torque and power peak numbers.
A hemi or steep inclined stem axis (SBC 23°) unmasks the intake valve toward the cylinder centerline immediately.
A shallow wedge (B/RB & Buick 15°, Olds 6°, Cadillac 11°) doesn't and needs lift to clear the wall.

Depending on whom you read, one of 2 events is primary:
1. most authors: intake closing point ABDC, which has no relation to lift
2. Vizard (and Harold Brookshire?): intake opening point BTDC, which has no relation to lift