I agree 20 or so degrees cooler than intake air is standard. So, if your camper is 72 inside you are right on target, if it is 82 you are beating the odds.
It has been my experience that no two of them function the same. Plus, your friend may have 15,000 and you have 13,500... in the same conditions theirs would be doing better.
Another point to consider their units may have a different level of insulation in the ceiling, that would make the greatest difference.
2011 Ram Truck 2500, Crew Cab, 6.7L CTD, 4X4, 3.73 Rear