Suppose...
Character A has 1 ton of TNT as his calculated AP.
Character B has 7.5 tons of TNT as his calculated AP.
By that logic, Character B is 7.5x stronger in terms of AP and he'd one-shot.
That's what I mean. It's only applicable if the stronger character's calculated AP is 7.5x stronger than the weaker character's calculated AP, and it applies only to versus matches, it cannot be applied to in-verse scaling since fictional verses have wildly different meanings of what multiplier it takes to one-shot. For example, Post-King Kai Training Goku was able to stalemate Nappa on his lonesome, but the moment Goku went Kaio-Ken x2, he effortlessly one-shotted Nappa and smashed his spine, leaving the latter paralyzed.