As soon as I've figured out the rules of the game, I hacked it and put this rule in to make it so that I can press the arrow key
into the crates because it's a lot more convenient that way:
[ No Solid | > Player | Crate ] -> [ No Solid | < Player | > Crate ]
But I wouldn't advise to include this into the public version, it's not in spirit with the first few levels.
I am fine with the size of level 7 but I just didn't like the "new mechanic" it introduced at all. Levels 8, 9 and 10, on the other hand, definitely look overly complex.