Here are the top 5 HR%’s for guys with 200+ PAs through 1919
1 Babe Ruth 1919 6.71
2 Ned Williamson 1884 6.47
3 Gavvy Cravath 1919 5.61
4 Fred Pfeffer 1884 5.35
5 Bill Joyce 1894 4.79
We know how dubious the 1884 numbers are (see next paragraph). And Cravath in 1919 hit 10 of his 12 HRs at home and in his career he hit 72 of his 87 HRs at home. Philadelphia was a great place to hit HRs.
Williamson and Pfeffer played for Chicago and their park had a wall that was only 230 feet from home plate. In all other years, a ball hit over that wall was a double. But only in 1884 did it count as a HR. See Clarifying an early home run record by John C. Tattersall. This article was published in the 1972 Baseball Research Journal.
Ruth's HR% in road games over 1918-19 was 7.67%. Again, that is far ahead of Joyce's 4.79%. We would need to know the road %'s of other players before this time but we don't have all of them. My guess is that no one is close to what Ruth did.