I'm one of those trappers who contends that a beaver almost always dives to the bottom to get under a dive pole. However, otter don't, and I am almost always trapping beaver and otter concurrently. In this case, if I have less than 10 inches between the bottom of the dive pole, and the top of the trap, I'll call it good. If there is more room than that I add a second dive pole, or a set of crossed sticks to fill in the gap, or cover the trap with a piece of brush instead of a pole.
Musher: If you set your traps in a channel, with the jaws 3 inches out of the water, how much space between the bottom of the trap and the bottom of the channel is acceptable to you? (P.S. That set wouldn't be legal is some states where #330s must be completely submerged.)