How does Circling Winds of Protection work? It seems with a Rego requisite you should be able to accomplish what you want. The target affects the form and Rego should tether it, so I think you're all good. Akin to the "root you in your saddle" spells I've been thinking over lately.
It the target was supposed to be the head, no dice. Then the form/target are off and we run into the reason most curses don't work for hermetics.
As is, I think you're mildly overthinking it, and there are some examples to back it up.
At some point, you're got to let the magic into the spell, the sense of power and wonder. I often get sucked into more rules debates than attempts to make magic come alive, so i'm trying to stop. I think the spell you describe is cool, is backed up be examples in the RAW, and should not be a confounding problem for hermetic magic in the same way a 'spell to make birds hate you wherever you go' is.
You're one of the foremost rules masters on the board, but I think in this case your desire for this spell is being second guessed by the rules-mind, possibly.
I suppose there needs to be a more defined set of strata for "allowed by hermetic magic RAW" vs. "judgement call/saga decision as to whether this is a violation of hermetic theory as constructed by the RAW" vs. "breaks hermetic magic's limits by the RAW".
My personal thought, given that spectrum has an element of judgement/opinion in it, is that the spell seems fine to me.
My two florins,