The tip regarding the non-playing hand is very valuable
@latej . Should I make an active motion with the non-playing hand, do I pull it back the moment I initiate the forward motion with my legs / hips?
Sorry for the late reply, I'm not at home and its hard for me to find a way/moment to focus ... ;-)
So, obviously the canonical answer is that the movement of the arms is driven by the movement/rotation of the body. That is also a correct answer, so it should not be disregarded, and, imo, should be always kept in the back of the mind... Actually, there is another thread about FH (I forgot which one now), but when read I was thinking it would be appropriate to say, the the proper form can simply be derived from observing, what your arms do, when you, standing relaxed and wide enough, simply rotate - you see what your arms "tend" to do... The key is "relaxed" and "wide"... However, when I wrote my first reply to you, I intentionally mentioned the non-playing hand, so that you specifically play with it, experiment with it - while knowing, that at the end, it is/will be an obstruction, because what I wrote at beginning holds - it is driven by the body ;-) But play with it, while keeping the other things in mind, you'll get there in no time. I'm sure of it. Peace ;-)
OK, and now, when I wrote all this bullshit, I want to add one two more things ;-)
First, by focusing on the non-playing hand, you may actually divert attention from the playing hand, and let it act naturally by itself...
And second, more importantly, it's necessary that your playing hand starts the motion with some delay after the body rotation and the motion of the non-playing hand. With this delay, your playing hand will want to make up for it - and accelerate properly... You really need to arrive at understanding this...
Cheers...