I searched all over the forums but I couldn't find a way to enable the large army (40 units) option in multiplayer. I played TW since the first Shogun, and I have a few frends with whom I especially enjoy playing 1 on 1 battles. The 20 units army was an improvement over the original 16 in the first couple of TW games, but after I tried battles with 40 units, it's kind of lame getting back to 20. I feel that a 40 unit army unlocks the true tactical potential of TW because it allowes you to truly have a first line, flanks, skirmishers and reserves which make the battles much more accurate.
But, the trouble is, I can't find a way to unlock this in multiplayer. When I host a battle it always gives me just 20 unit slots to fill while in SP custom battle there are always 40 slots. Solution? Anyone?