Yes! Now the arena size is perfect. I've got 2 ideas:
1. More bouncing force for arena and survival.
2. In arena mode, the player that stand at the centre without take risks can easy win. The solution is to change the aim of the game: unlimited lives and 1 point for the player that knock out a rival. The winner is the fist who reach 5 (eg) points or also, if you like, who get the highest score after a limited time. In case, just remember to include score draws possibilities or else, because 2 or more players can knock out the some rival at the some time. Dunno what is the best choice about all this, but the score system is important. Agree? :P