This rune increases "bow distract range", but I can't find what that means. Is that the range at which you can cause an orc to come investigate with Right Trigger and Y (or R2 and Triangle)?
Bow distract range refers to the "distract" function of the bow (LT and Y). It functions similarly to stealth attract, except in reverse; nearby Uruks are drawn to investigate the spot that you aim at when using distract.
There is a similar rune that increases stealth attract range.