Lend me your brains

This is because you are using the same chain length for both ratios, my set up would have the chain length tuned specifically for each ratio.

Sir, I refer you to my previous point, and provenrad's comment.

Essentially what we're saying is that tuning chain length is not as easy as it sounds if you want to avoid having a slack chain (and you* do* want to avoid this).

By the way, this does sound like a fun idea and should be fairly cheap to try out, even if it doesn't work. I'm not trying to sound negative, hope my comments don't come across that way!