Yep, I get a fair amount more head when on the last couple of liters, I pull the gas QD off when I know it's about to happen, I know my system pretty well so within the space of two or three beers I know it's comming. Also have the issue with a very full keg not carbing to it's full potential till I pour a few. Only time I've fiddled with my reg was when I got a micromatic recently (issue pre-dates this), and when I first set the system up over 12 months ago. Be good to know a cause of this but not too concerned about a fix as it doesn't bother me, maybe cause I don't know any different though..