I am assuming that 5/8" has the arrow below the nocking point, if you are shooting split, you may have a heavy ring finger. That would need to be adjusted if you shoot a fatter diameter wood shaft. I cannot help but wonder what the upper and lower riser fadeout to the string would be on that bow if all else is quite normal. The higher BH could be needed if the arrows were very stiff or if the grip is getting torqued, which is a possibility if the string never makes arm contact in a more normal BH. John Schulz suggested 1/16" up on his nocking point, nocking the arrow over the nocking point, Ekin said about 1/8". On bows that have the 1/8" less measurement on the bottom limb fadeout to string measurement, the nocking point works out to be just shy 1/8" above level for me with parallel shafts and right at 1/8" for tapered shafts with old style Mercury arrow nocks.
Some bows can have slower cast with too much BH. John Schulz said that it could be as much as 20 fps, we experimented with this some with one of my Schulz bows. We found that increasing the brace to 1" over what John suggested with Acme cedar arrows that flew good at the suggested brace, did not lose 20 fps second like John said was possible, it lost 8 to 10 fps. On another bow that had a suggested range of 6&3/4" to 7", Primal Styk, going from the top of the suggested range to the bottom, then to going under the range made very little difference. It obviously has something to do with how the limb loads and unleashes its energy or the difference between a B55 string to a modern string.