Except that you cannot eliminate the "5 levels less" options. Even if you boost your bounty level up to +10 above your current level, the AG can still assign bounties for creatures -5 levels from your current level all the time. Centaurs are level 23, so you will be getting random bounties for them until you're level 29. I've taken probably 4 characters to hunt in the quiet caverns in the past couple years, and always get those pesky bounties... The grutik and undead trolls are rich though, so it ends up being a minor inconvenience to just abandon the centaur bounties.