I finished the level later on. It was a lot more simple understanding that it used the mechanic from the previous stage. And it's all right if there are challenging levels in a puzzle game, especially considering it is an option stage.
Regarding your question, i went back to all of the non-optional stages for review, and from what i remember those were fairly straightforward. That being said, i also have seen part of the game before in a youtube video, which might have helped my decision making in those stages.
I will let you know if i find out about something later on in the game, after all i haven't even progressed with the main levels that far, insisting on finishing those optional stages. (fulll circle and self-sabotage seems really difficult too, i like the challenge though)