You're right: this is a well-known trick for the veteran player. You hit the nail with the intended solution, despite the embarrasing backroute that Raymanni easily spotted, much to my annoyance.
As I said to Raymanni, I've only made a few original levels, so it's comprehensible they are still not very hard, since I'm still a novice
. However, I think the two I sent to the contest would be interesting and tricky to solve within the old engine (DOS/Lemmix), which offers no help at all to the players.
Also, I agree with you and Raymanni about the austerity of the scenario: I'll add some more extra decoration and fix the backroute in the next version. I'm afraid I can't think of anything to improve the difficulty: at least, I hope you find some challenge on the -somewhat- not trivial moment to increase of the release rate