.....are you using caffeine/energy drinks to aid the O2?....I found it improved effectiveness dramatically if powered down immediately when a hit felt..
....i am also one of the advocates of hitting the oxygen immediately and paid the price often if i could not get to the tank soon enough....BUT, over the years there were cycles where i HAD to WAIT until the hit got to a Kip 2 (not 1, not 3+) for it to work...and it would. strangest damn thing that i found by accident, after much panic that the o2 wasn't working any more. I have absolutely no explanation for it, but I do know that clusterheads have an innate feeling for their own cycle that others can't fathom. go with your gut....
best
jonathan