When i first read this i was going to reply about air density as well, but then i thought about it in practical conditions.

Changing from 10 feet to 20 feet will not have ground effect, air density or air temperature affecting flight, but it still does take more power\pitch to fly at 20 feet versus 10 feet, correct?

I am not sure, i know it takes power to get up there, but once up there can you put it back in hover power\pitch range and stay up there?