I reckon which mechanism of preservation the fuel stabilizer used (assuming there's more than one known type) would be the key. I keep thinking of preservatives which grab oxygen and bind it to the preservative substance... Greater dilution may mean less effectiveness since there would only be so much preservative that could molest so many oxygen atoms.
My memory ain't what it used to be but IIRC food preservatives such as BHA, BHT, TBHQ, propyl gallate, etc. work on this principle. Funny thing, too- I just remembered a short article in one of the auto magazines some years ago mentioning BHT as a gasoline preservative- just throw in a teaspoonful (or was it a tablespoonful?) and it would help preserve it. Me wonders if Sta-Bil is just liquid food preservative? Kinda smells phenolicky to me.
Sorry I got off on a tangent- I'll probably just triple the normal FP3000 dosage in my '77 Chevy 454 truck- it likely won't hurt it and I've got four gallons of FP3000 too.
