This is rough and incomplete, but it demonstrates a different direction:
Channeling Nature is a part of what we call “mustering dice” when you try to gather up any additional dice before the roll. You can spend a persona and add those dice provided you have the persona to spend. It only costs one.
Acting Outside of your nature (substituting it for a skill and not using Beginner’s Luck) does not cost a persona, but you are subject to tax.
Maybe think of it as stages of the roll.
Do you have the skill?
If not, do you want to use Beginner’s Luck?
If not, are within your nature?
If not, you are subject to tax if you fail.
Then comes the stage for mustering dice, where you can add it dice and spend a persona to Channel nature. You can do this provided you have the persona.
Once more, you must ask if it is within or outside nature, and again you must assess if tax could apply on failure.
Finally, you assess tax and apply it if necessary.
If you test Nature in a situation not covered by your descriptors and fail the roll, reduce your current rating by the margin of failure (to a minimum rating of 0).
If you channel your Nature for a test not covered by your descriptors, your Nature is taxed by one if successful, or by margin of failure if failed.