Sorry, try this one:
(Overheat / 6) * (max(WeaponLevel,100) - 100) ^(1.5 * ((max(WeaponLevel,100) - 100) / 10) /2)
That seems to have done the trick!
Thank you all very much!
I think I also found the source of the glitch.
So I have this object that stores the WeaponLevel on all weapons. Now the issue is that I had them on all three layouts, which resulted in three of them being active on a layout at once (because they were global and also had the behavior "Persist". Going into the debug mode, I saw that one of them had the default variables (every level on 0) which was probably the issue.