It is not so much in the direction of rotation of the prop. I tried that too and did not gain anything measurable.
It is more in the fact that air does not scale down, and as weird as this may sound, air is too "thick" to fall for this trick.

I tried similar in several different ways, and never got any measurable difference, UNLESS there was an extensive airscoop of sufficient dimension to force the air through the fins.

Flying, it will work better, but on the bench, no way Jose, that darned air won't go where you want it to be...

I found that in cowled engines, what made the most effect, was air deflectors in front of the air EXIT, creating a local low pressure zone. That seems to be way more effective, although I cannot explain why.

It's just an observation, just a thought.