Use The Force, Luke! [8D]

I think it's best to start with a gap aiming system, as described by Hill, Schultz or Byron Ferguson. As you get more experienced, you start paying less and less attention to the gap, until you've finally become an instinctive shooter. Then when you change to a different bow or arrows, you can fall back on the gap to figure out how the change affected your aim and get yourself back on track again.