Steve I never had to tighten the nuts on that. I have on a couple of others but each of them it was only a one time thing. I find the plastic heads seldom, if ever, need tweeking once they are set. My general rule of thumb for tension is this
If I can push on the head & it gives just a very slight amount & the feet are flat with no sag (but not conversely bowing)Then I'm good to go. If it starts sagging then I tighten to the same rules as above.

if as I tighten, I see the bridge rise & the top is beginning to get convex (or higher under the center foot) I back off cause it's getting too tight
I believe if you tighten the head every six months that will be way too often
I just don't want to see you pop it again.
Charcloth