It was always my understanding that in order to perform an accurate cylinder leak down test that the piston must be at TDC for each individual cylinder with both valves closed. If you hear air escaping from the exhaust you have a bent/cracked/not seating exhaust valve; if you hear air escaping from the intake system you have a problem with the intake valve; if you hear air escaping from the oil fill hole you have either bad rings or a damaged piston.