I would suspect that there is little variation in the constant rate.
It would also be interesting to see how Hauser's Law works in even more socialized economies such as those in Europe. Again, I suspect that the empirical evidence would support it. While some cultures may have a higher tolerance for taxation (and others a lower tolerance), and while the rate may vary by a couple of percent more or less according to these cultural tolerances, human nature is to maximize individual benefit.
Some of those old enough to remember might recall Nikita Khrushchev's grand experiment of allowing collective farm workers to cultivate a private plot of perhaps a half acre or so per family in the 1960's as a means to address Russia's chronic shortage of agricultural production in the world's largest land mass.
These private plots made up something like 3% of the land area under cultivation but produced over half of the saleable produce. It turned out to be a major embarrassment for the Communist Party, but they were afraid to end the program as it was the only thing that kept the country from starvation at the time.
“The avoidance of taxes is the only intellectual pursuit that carries any reward.”
(John Maynard Keynes)