I agree there needs to be some tweaking done with the damage of beams and their falloff/optimal range. I have noticed a slight decrease in damage even within the optimal (under 50% max range), but I am not here to comment on that. I kind of agree with OP idea on beam optimal, but I think for a game we shouldn't bring too much current technology and Physics into it, since after all this is set in the distant future. I think having that "most optimal" range where you do a slight increase in damage at the beam's "most optimal" could be a good idea, but don't think the damage should decrease from "most optimal" to 0.0k.
There are two buffs that should be looked into though. Example is the AWCS and Intolerance:
Those currently do not stack according to what I've been told in game by a few people, and I believe was verified with a GM. Since we now have optimal range and falloff range for beams, I think "beam focus" should be a buff to increase the optimal range of the beam. So say, a device like AWCS could add 20% to optimal range or something like that, thereby increasing the base distance that the beam will do 100% damage (haven't ran numbers, just using the general idea).
I don't want to make this too long so I'll cut it off here and see what people have to say.