I was referring to grouping with the same level players, or similarly leveled. Within 2-3 levels I haven't seen much of an xp nerf that you're referring to. A level gap, of say 5, yes, there is a BIG hit to xp. My opinion is that it's there on purpose to keep people from power leveling "lowbies" through stuff. I think it's a good policy to have.
I just ran a random group last night, my first one since returning to this game, and the group finder put me (19) in a group that ranged from 16-22.
The group XP for any random should not have a power-leveling correction in effect. Period. If it puts me in that group, that run needs to be worth my time. That means I need to get a reasonable amount of XP and credits per hour, at least comparable to what I would get questing with my time.