How important is it to have FLV left hand at impact to be able to execute the different hinges?
If a player has a turned left hand, that will affect the face at your checkpoint.
A Flat Left wrist is very important, even with a Strong turned left hand as a grip. Think of Flat as "not cupped" at Impact. What is important is the shaft and left arm being in-line. It forms a back-side Flying Wedge. It could be seen if you extend the shaft line under the left arm. This rear flying wedge is in-line at Store or Release, 8-9, in-line at Impact, 8-10, in-line through the Hinge Action to Follow Through, 8-11. Regardless of grip. That is the rhythm of the RPMs and acc#3- Transfer Roll. Transfer Roll is Arm and pivot produced.