As Topic.

TDC

A few degrees after TDC, to mimic the position of the piston when there's maximum cylinder pressure, IF you can lock the engne there. If not, when you pressurize the cylinder, you'll spin the crank.

Otherwise, TDC

bdc cyclynder will hold more air,and since its already down it can't rotate crank.Make sure rocker arms are loose so the valves stay closed.

@Bdc i got 20% Readings.

@Tdc i got 5% readings.

middle of them i got 10% readings.

On a cold engine. Anything wrong with that high leakage @ BDC?

All air going down. Nothing through my valves.

5% at TDC is good. For future reference, TDC is the commonly accepted "official" way to do it. If you are at TDC, the engine won't turn when you apply the air.