This number is related to the numbers of virtualized units that will spawn at any time. Changing this value can create strange behaviors such as enemies spawning up on your back or front so it is not recommended to change. Active Limiter is not related to HC

I have a method (I do not know if it's the right one) to evaluate if HC is needed. First watch the fps of your server when you are in a medium or large city and induce the enemies to enter combat, you can use Zeus to do this by placing allies or enabling invisibility and fire at any direction without stopping. If your server's FPS drops too much to something like 20, HC will be needed.

I hope it helps in some way