I think that rule 6.4.
6.4 - In a 3 server battle the victor of the centre (1 server as centre, 2 as flanks) always wins the battle outright, therefore their is a limit of how many troops can be deployed to the centre - 30 per team.
Should be a bit modified. There could be some advantages when one side wins the center, for example, they will know placement of enemy soldiers on flanks and could choose to which flank join, or split and join both. But outright win of whole battle, if only center wins is a bit OP a think.