Hi Fiver Rah!
Thanks so much for playing the game and all the insightful comments and ideas. That's so valuable!
I will definitely experiment with your ideas on how to change the mechanics. Yeah, the main concern is to maintain solvability, but I really liked the increased radius and sensitive spots ideas! I think that could really work. As soon as I have something done, I'll post here again.
Btw, I also found the higher game levels surprisingly difficult!