What happened is this. The slider has been set to 48 bots so once bots are 47 or less (48 when with player), the slider should work fine.
BUT
The aidefault.con in ai folder for fh2 is set to 31 (32 when with one player). This descrepancy is the issue.
Setting it to 47 fixes that.
If you want more than 48 players, you are going outside what Dice wanted, so you need to bias it by adjusting the ingame toggle after setting the bot count in aidefault.con
Since 48 is the normal i.e almost 50, adjustment is easy.
64 bots at 50:50 ratio needs the slider to be at aproximately 64 to restore.
The max bots you can have is about 100. Even if you dont care for balance, the squad names run out, so you would get extra bots, including players not getting squads.
The aidefault.con needs to be fixed by the devs to agree with the ingame slider ie. Set to 47 rather than 31.