What SNG limits have you been playing at? How often do you play more than one SNG at the same time, and how many do you simultaniously play? What site do you play on? Tell me about your competition.

I can't account for your numbers, and 300 SNGs is too many for the luck factor to be killing you. You've got a real baffler here, unless the following two things have happened:
(1) You are going to a maximize-ITM style of play
(2) The ITM effects are being destroyed by an increasing quality of opponent.

Needless to say, the better your opponent, the fewer 1st places you would have.