maybe it has something to do with cooling since the lancer has 2 size 2 coolers? or maybe just a bug? shame though cause i'd be real interested in a small ship that does well in atmo with a size 2 q drive.Okay, did a bit of testing. Even though you can put a size 2 Quantum Drive in an Avenger, you don't have enough Quatum Fuel to jump very far. Also, Freelancer gets much better mileage, what would have taken an Avenger 720 QF to travel, only took the Freelancer 560.
edit: have you tried running the q drive at something like 3/4 power and see what it does?