Just, fly like a sissy.
I've been in La-5FNs against "Super Brewsters(FM2s)" a LOT!, in the Fin-Rus setups in the CT.
Well, for anychance if a FM2 is behind you:
* don't dive away
* don't try to rope it without a MASSIVE E advantage
* don't turn
* don't expect to live
Unless you have at least, initially more than 600 yards distance, you're probably gonna die. If you have that distance, than ram up the throttle and WEP, and slooooowly jink, and pray that those 800yd .50 shots will not seriously damage your plane.