Same here. On my knees I do 2 sets, each set at the moment is 10 reps of one arm and opposite side knee using the "empty" limbs as little as possible for balance and a wee cheat, then immediately 15 reps with both arms/both legs. I flair the angle to maybe 30-45 degrees from directly above shoulders to get more of the clavicular head of pecs involved. And oddly, my goal is 2X20 as well.