I think it might be an idea to just remove the ban completely for disconnects/crashes/leavers and just have it for people that are reported AFK. It would be nice if it only applied the ban for people that forcibly leave battlefields by closing their clients but unfortunately it's not possible, it's all or nothing - the game can't really tell if you closed your client through the task manager, or if your internet went down or you crashed etc. etc.
Just trying to think what happens when a match doesn't have enough players to continue because somebody leaves - does it end in a draw or do the side with the most points win? I'll need to check all that first, because I can see people abusing it.