it also depends on the vehicle. more ethanol means more absorption, up to 90%, but we don't know how much is systemic and if it grows more hair.
have there been any hair count vs concentration studies? I just know of 2% vs 5%, and we don't know if the PPG gives a slower delivery and that is the reason. The 2% has a higher rate of absorption, percentage wise. I'm not so convinced the concentration rule is true. I don't know if we have enough information to know.
And 5% only regrows 50% more than the 2% rogaine. I'd like to see some more studies.