Originally Posted by
Stone215
Certain types of boost, generally those that make something smaller, fewer or shorter(i.e. "fewer casualties", "shorter upgrade times", "less time till your health refills") have diminishing returns when there are multiple sources of that boost on your account or faction. What that means is, each new source of that boost that you add is slightly less effective. So for instance if you have a 5% health regen boost effect and then another 5% health regen boost is added, you would see a total boost effect of 9%.
This is intentional, because these boosts cannot logically go below zero. It's impossible to have faster-than-instant upgrade times, for instance. Or to have a casualty rate modifier so low that you actually get units back. So for these boost types, we have the diminishing returns effect stated as above. New sources of the boost will still add to your total and progress you, though. Boost effects that ADD something (more attack, more defense, etc.) theoretically have no logical upper limit, and those stack normally (5% extra attack boost + 5% extra attack boost = 10% extra attack boost.