Just remember - most Ramachandran outliers are due to errors in the environment - eg: maybe some side chains clash hence refinement tries to move things to accommodate that bad feature, etc etc etc...
At that resolution it is inevitable you will have some level of mis-interpretation ..
4% outliers does not surprise me.
EDSTATS is a useful tool to find things such as pep flips - you can access it most simply from CCP4 GUI2 .
But unless the outliers are in a important part of the structure I would suggest checking, then living with them.
Eleanor