If you guys want some serious 109 kills, keep the I-16 at low altitudes. Try to get the 109s into a turning fight, then if that works, you should have no problem either breaking away from them, or turning into them, and getting a kill. I've done it, and it seems to work. Hard part is, getting them to turn with you, but the second they go to climb away, get them in your sights. Their speed from turning around and around will have dropped, and they'll start on a slow climb, that's another chance at filling them full of MG and Cannon rounds
Good hunting.