I have a Tri-Point metal AST and I am flushing my coolant system. What I noticed was that the cap head of the AST has two notches, one allows the cap to go on, then you have to push it and twist it past the notch, then it can go up a bit and the lip on the tank stops the cap from coming off, however, if you push it down again you can get it on a second 'notch' that presses it very tight against the tank....I originally had it at this spot, hard against the tank.

My question is, should I have it sitting in the space between the two notches? Might it be unable to sepearate air properly because its to tight against the tank?

Upon comparing with the stock AST, I think that it does need to be tight (on second notch) against the tank head.