I understand the graph, but I think that the HR/PA ratio compared to league average has some issues. Like park factors, you can't assume that everyone will benefit equally from a significant change in the baseball environment. It's not surprising that corner outfielders with power benefitted more from a lower mound than slap hitting middle infielders that didn't have the power to hit HRs no matter how flat the mound was. It should help each player's rate rather equally. Yes, a 30 HR hitter might increase to 40 HR, but a 3 HR hitter should still increase to 4 HR. It appears the slugger got more help, but the slap hitter got the same help in terms of rate. So in comparing the rates, I think we are fairly okay there. It might be a minor concern. And, of course, I think it's a mistake to apply one cause, PEDs, to the increase in HRs in the 1990s. Smaller parks, better scouting, better physical training (apart from steroids), teams willing to play bigger players in the middle infield at the expense of defense, expansion (including a ballpark in Denver), etc. all contributed to the HR explosion. There is no single factor that effected Aaron that did not effect the rest of the league just as much, unless he led the way in an increased level of physical training when he was in his later 30's.