I started out with the bottom hand aligned with my armpit when in deadhang. This was my initial understanding of the required distance, however it was very difficult and I hit a plateau at around 4x3 reps.
After re-watching the video it seems like the athlete's bottom hand is distal to his shoulder, somewhere around the top of his bicep. I tried it like this, and the pull was much easier and I've broken through the plateau.
If it's easier to picture it this way, before the change my bottom hand would be below my hip at the top of the motion; now it is perfectly aligned with the hip (both instances top hand is pulled into the chest). Which is the proper separation?