What Wolfgeorge said..it is (as you noted) hard to test the optimal air seal..what you can do to improve it is:
1) if you have a PCS valve, unscrew it, teflon tape the threads and screw it back
2) If you have a PCS valve, notice there is a tiny small Allen Screw that keeps it in place, because with movement, shooting etc. it could get looser/tighter (although teflon tape kinda helps securing it in place)
3) Do not pull the bolt-to-magazine round rubber o-ring, because it will get ripped when moving the bolt..you could reinforce the magazine valve spring, which is the one that pushes the round brass cylinder (right on top of the magazine valve) against the bolt valve. I made some custom springs from normal springs bought at a DIY store..commercially you can buy the G&G Gas Route Connector Spring, which is stiff-er than the original..but if you want extra stiffness you should custom make one for your magazine. Be careful when testing it because it might cause your bolt to be stuck, when to strong.
4) VSR-type bucking can grant you a better air seal, I have the King Arms nozzle and the VSR Hop Up Chamber Conversion and all in all it is a more-proven system.