Conceptually very cool! Finding the solution to the puzzles is quite cryptic, though. The second level has at least two solutions when talking about matching the character's size, but only one of them is valid. Is this because the order you collect the notes has to be a specific sequence? I got stuck on the fourth level, too, with a similar situation where I "solved" the puzzle with the correct size, but I must have collected the notes in the wrong order. Some kind of hint about the correct melodies would have been nice. I noticed an icon in the bottom right that changed as I collected notes, but I wasn't sure what it was supposed to represent.
Nonetheless, this puzzle game has potential. Neat idea!