The mass cost, and capacity for the e-storage was initially chosen as some value that seemed reasonable at the time in order to use the ACU vs t2, t3 and experimental units, with a consideration to how granular this investment needed to be, that means, how much mass needs to be spent to enable overcharge in the first place. Currently we're doing 5 damage/mass invested in e-storage, and the damage maxes out at 15k for 60k energy which translates into 12 e-storages or 3000 mass. Now let's see how we could tweak auto-OC fire rate and change nothing else.
I'll pull a number out of my ass: say that 2 storages should only give you 30% auto-OC frequency. that means 15% fire rate per e-storage, with a cap at whatever multiple of 15 you want, or 100% of manual-OC firing speed at 7 e-storages. how's that ? you get to AFK your ACU if you put in around 1500 mass in e-storage. you want a bigger tax? make the ass-number 10%. All that research I did and showed in the first paragraph was useless. The math, trivial. Impact on manual OC, almost none, aside from the fact that now, lazier players incidentally do more damage with their overcharge, but that's sort of irrelevant at t2 stage and I can't see how this side benefit would invalidate the whole idea. Just make 3x more e-storage if you want auto-oc to be as good as it was, easy to remember and hopefully, easy to display in UI, along with whatever else you feel is obscure about OC right now.