First of all your calculation seems INCORRECT. When the Steem price decreases the pay out also decreases. Or do I just have that wrong in my mind?
second of all I would say you need to calculate the ROI in SBD. ROI = return on investment. And what did Max invest?
Third, if I calculate his return in SBD or in USD I get a return of 9.32% instead of 7.32% assuming prices remain stable.