This picture.
I was hitting the wall yesterday, trying to understand the body kinetics and searching for the best options. And then I came consciously to what workes best for me so far.
I found it very important where is the position of my behind leg.
For FH it's for me somewhere between a neutral and a semi open stance, I guess closer to neutral. But what's important to me is that my legs are spread, with left leg (I'm right-handed as well) staying forward, and weight being on the right leg which is significantly behind. With legs being spread my body is positioned little lower just like on this pic. Then takeback, weight is still on the right foot. When I start to swing the best I can do is to start transfering the weight to my left (fore) leg and lean a bit forward, while performing the hip rotation coordinated with weight transfer to left leg. Some wrist lag for the speed, legs spread. In the moment of contact/impact body stance is open, weight is fully transfered to the left leg, body is leaned forward, and right foot lifted so I only touch the ground with the tip of the leg - the result of a weight transfer and hip rotation.
For OHBH the best I can do is to ensure that my left leg is behind and on the right side, just like on Wawrinka pic. Stance is completely closed prior to swing, weight is again on the behind leg (now it's the left leg of course), and legs are again spread. I feel the best when I put my left leg pretty far to the right. In the swing its again the same, body/hips rotation and weight transfer to the fore (right) leg, lifting if right foot to stand on the tip, in the moment of contact finishing on a neutral to open stance, I feel the best when finishing the swing with my body slightly leaned forward.
Anyway, I found that for both of my shots the most important where is the position of my behind leg in the preparation, and that I like it pretty spread from the front leg and enough behind.