"allthings being equal he is twice as big as that croc."

Yes, and the 5m croc is almost twice the length of yours. That was my point in showing photographs of a smaller one leaping out.

I've seen smaller ones still clearing the water entirely, tail and all. But they're small. The larger they get, the less they can jump relative to their body size, in the wild or in captivity. Yours will not clear the water to his hind legs when he's 5m long.