Hello
_BlackKnight_ In Defaultstats.xdb there is a section about AI. There it is declared global limits for AI hiring. For example:
<HireHeroesBase>1</HireHeroesBase>
<HireHeroesPerTown>1</HireHeroesPerTown>
<HireHeroesGlobalLimit>14</HireHeroesGlobalLimit>
This means that maximum amount of AI controlled heroes on the map is 14 no matter how many players there are. So the less AI players that remain the more heroes they can hire. Of course there is also a limit of one additional hero per town I think ( though I never tested if it actually works properly with the advanced AI).