OBj works the same way for bombing as ENY does for (air) combat: The lower your bomber's OBJ is, the less perks you get for destroying the same target.
So the bigger the bombload is you are carrying and the higher the OBJ, the more perks you can get out of a single sortie.
To show the theoretical perk gaining capabilities of the formation bombers in AH, I simply multiplied the OBJ rating with the max amount of actual explosive power a bomber can carry:
The higher the resulting "BPF", the more perks you can theoretically get from a single sortie (for example town miling)
Of course, in reality this theoretical value is very much influenced practically by a bombers survival rating.
As you can see, the BPF of the He 111 is already very low, and if you then factor in the much lower chance the Heinkel has to making it's way to it's targets (and back) compared to a B-24 or B-17...
Or mabye the best comparison is He-111 vs B-26. Both carry about the same amount of ords (8x250kg vs 8x500lbs), but in comparison the B-26 climbs like a rocket and runs like a sports car while carrying a substantial defensive punch. But He 111 OBJ is 10, B-26 OBJ is 18.
You actually get
punished in terms of perks for taking the 'worse' plane. It's almost as if the P-39 had a lower ENY than the Spit 16
