It is based on the estimated effectiveness of the plane. The ammo loadout, ord load out, fuel load, and the planes real capabilities compared to others, and the time it was used in the war. These all have a factor on the eny # it is given. While some planes could be disputed. I think the scale is very quite accurate. The yak3 holds and retains E better and turns better, so it could be more effective in the MA. Idk, most say that plane is a beast, but Im not that big on yaks.