I thought they were on the 5s, e.g. Bald Knoll is 45. I know that last one for a fact as I was just there, but I think the pattern follows. L1 camps are L5. L10 camps are L15. Etc. If you're at the recommended level and no more than ten levels above you receive the entire bonus XP reward for completion, in addition to any XP from slaying mobs, so Horizon, Tranquil, and Bloodshore would be ideal for L25.