The condition you are referring to can give you a false good idle, but it won't affect full throttle performance as the lsn is completely bypassed at full throttle. The general consensus is tune hsn first, and it's very important to get the engine fully up to temperature before tuning. I personally like to start from rich, lean hsn until it starts to cut out at full throttle then richen 1/8 turn. I do a few full throttle passes to make sure I've richened enough and I'm getting good smoke and top end. Then I do the pinch test to get the lsn into the ballpark, then test throttle response until it takes off with no hesitation(rich) or cutting out(lean). Then I lower the idle to a nice steady gallop.