Nope, not that either. It's a combination of speed and distance.. forx example, i've dropped bombs in an IL2 (IN AH! not in IL2) around 600ft -from target- -in a dive- (albeit only around 250mph) and they havent detonated. I've dropped bombs from the Stuka in a high(er than the IL2) speed dives, released under 500ft and still had them detonate. (In a dive, almost straight downward in most cases so it couldnt have travelled any more distance than the (for example) distance tag's specified).
So I think it's a bit more complex than just distance.