I agree with Jim OAK greens are xtra fast- downhill- compared to Congo, Kia, BPB, for instance. Pretty comparable to OLY and Merion however. Like the latter 2 Open courses, the general rule is "stay below the hole" however below the hole isn't always "short of the hole" as is typical of Merion and Olympic= sometimes it is left, sometimes right, and even behind the hole on OAK. It is something you learn over time.
Having said that TH, given your ranked rounds over 400, you should have better stats vis a vis putting in general. Only 1/3 One putts is quite low- u should be at 50% or better at this stage. I suggest you look for putting tutorials by the likes of StoneCold, Buggyyy, Notonthis and others in the forums and on youtube. They should help a great deal to understad the many subtleties of becoming a good putter, and those stats will improve quickly.