I have an idea for that, Have alternate pathways for some of the maps that are only get unblocked when players reach X amount in a server, these new pathways allow greater attack angles. Have derbies block them until enough players are in the server. This would only be needed on some of the maps that end in stalemates way to offen, such as field.
A good example would be a new tunnel on field that goes right behind the two refineries, not protected by base defences at all. they would be blocked off via boards or something artistic, maybe doors that open up? completely until say 30-40 players join at which point players can destroy the debris or the doors stay open?
Or a map settings based on players in the current map when it votes. EI, when server is changing servers and there is 30 players, then load the edited version of field that has more attack routes. if its less than 30 then load the default field map.
What you should try to do is mange attack routes based on players playing, more players more attack routes. 100 players will not work well on these current maps, they need to be much bigger. 5 players per tunnel, 10-15 per tank battle area.