if he mean AI units,then listen:
Max AI units: 100
using pick every unit > attack target, this number will be lower by 10-15 %
using guarding constants options (guarding area + time of moving back) will improve this number by 5-10%
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P.S. at russian forum several men say that if make a lot of groups ,12 units in each group, than AI may work properly even with 150 units !