Difficult balance (hard mode)

[OneEyE]

Its easy to play alone. But its hard to play with 2, 3,...8  player. Iam not sure why but it feels wrong. The idea behind is, i trying since hours to get into the full16 player server but no chance. If i play on a empty hard mode server, sometimes people join but we only get to the first waves and after 3 or 4 attempts the player leaving frustated the server. So its not possible to fill the server with enough player.  :-\
I think we need some balance fine tuning.