Interesting thread, and some good information. I don't recall doing ground rows in F1 a few years back, I thought PE1 was hinge rows. 5 x 10 of those were....enlightening. And mastery now is 5x5.
@Michael Knight's suggestion of using more advanced elements to progress is a good one: I've been stuck on FL/PE5 for a while, yet PE13 is easy. The mobility is what kills, though.