Key things:

Index finger is the primary finger for rpb… I found this to be very important. Also another thing I think is different with rpb and shakehand backhand is the elbow position. Usually rpb is lower. Compare Felix Lebrun and Jun Mizutani for example

Also, Fang Bo said that Wang Hao has the heaviest loop ever (heavier than Wang Liqin, Ma Long, Ma Lin etc.)