Just tested it out and indeed you can get out of the situation where all 3 spaces are taking up. The draw back it has unbalanced the game a bit and i just scored north of 6,500 and feel i could roll it over so to compensate maybe turning the enemy speed up by a full 40-50% at level 7 :). The speed its at now is perfect for level 6 though
Viewing post in Tomy Sky Attack
I think the problem is the speed of the enemy missiles, which remains the same throughout the game. So what I've done now is made the enemy's missiles speed up slightly with each level. You can test it out on the public release.