I love this! I did a puzzle game where the main mechanic is changing the size of boxes too but I'm a big fan of how you implemented it here. The idea of only being able to change the size while looking through the glass makes for some really fun and interesting puzzles. Your puzzles are designed really well where they weren't too hard or too easy but the perfect space in between where I feel like a genius after I've solved it or as soon as I see a possible solution.
Great job!