As we all know, currently its working wrong:

Quote Originally Posted by Cordovan View Post
We are aware that the Reaper XP penalty is based off of the non-adjusted Base level of the quest or raid. There has been confusion over the issue, but we're all on the same page now (at least I think so). We are taking a look at people's feedback, but it's too early to say whether any adjustments will be made in the future. We are also looking at some discrepancies being reported involving Reaper XP in Epic level quests, and will be most likely working on a patch to correct this as soon as we can get it out.
It makes grouping harder:

Quote Originally Posted by Vindraxx View Post
Has this been discussed/reevaluated at all since this posting? This seems like an incredibly awful barrier that makes grouping level ranges much more narrow and I personally would like to add my voice to those that have expressed making reaper exp based of the adjusted base level of the quest so it is in line with Bravery Bonuses. It makes zero sense to me that these systems are not congruent with each other segmenting those who want to run at "base level" for max reaper exp and those who are at "quest level +2".