If I remember, tomorrow I'll go out and measure my runners. My drake is taller than my hens but that might be because he's a white and they're various colours.
Taller than the average duck, for sure, since they stand UP!
I doubt the runner will trample your hens. I find that my birds stick with the saying "Birds of a feather flock together" and they stay with "their own kind". I don't house my chickens and ducks together, but that is what happens when they free-range.