It might be that in location A, provider Q would have the strongest
signal at an appropriate price, while in location A the user's device would elect provider Z's signal as being adequate in strength and offered at the best price.
At least as important as the tax level is the commitment to keep raising the tax, preferably annually, so that energy - critical decisions, from car - buying (Hummer vs. Prius) to home - buying (exurb vs. transit - oriented community) to factory locating (highway interchange vs. rail line), are made with carbon -
appropriate price signals.