Uhhhh.. I believe damage is a bit more complicated than that.

ive check some videos about ship damages and ive done this and it gets around to that number with out the crits etc

That formula consider if you have full deck shots or full belt shots.

As soon as you get the mix of these two, it's really complicated and considering when you fight, you get much more of the mixing than pure deck shot or belt shot.

I dont think max angle has anything to do with damage. Usually I find that at angles of 0 degrees deal more damage than other higher angles. Ive done over 7000 damage per shell with crit once in a KM BB2.

Not really the best answer but ok.
Bismarck, Vanguard, QE, Hood do more damage when their angles are lower in general.

Some guns hit hard at max range, some guns doesn`t hit hard at max range but do by lowering their angle.
And in some case, low angle shots do as much as high angle shot.

There`s really no general formula especially with NF. Each gun has its own characteristic.