Questions such as this would probably be better asked in the Redpill Rescue section:
http://forums.station.sony.com/mxo/....m?forum_id=121
Just for future reference 
To answer your question, though, while I'm not sure what the actual % is there is a huge difference between the XP payout for different difficulty levels. I'm guessing easy probably gives you somewhere in the neighbourhood of 25% of what you get on hard.
