The prop gov has it's own pump....
It don't start pumping till the engine starts turning.....and the "pump's" speed, (thus it's efficiency), is directly related to engine speed up to idle.
Think about that for a second or two.
PT6A-27 48% NG idle in feather, with 52% NG in full fine sounds quite normal to me and that is what they taught at Flight Saftey. It is what is in the book also, (unless it has been changed recently).