You’ve picked a very good option in the Chin Rack, if you can pick a line where the srtart resembles an OH press and the finish resembles the squat (back on bar) don’t worry too much about hand positions but try the one where the biomechanics are right (for you), the important part is where the upper arm is, gotta try and get the upper arm past the torso line for a complete contraction of the lats