no the L relationship should sustain.
not ulner deviation.. it's supination.
you know what, borrow this concept from the FH... Oscar says address the ball with the leading edge, not the strings.
same idea with the BH... you want to upper-cut / side-cut the ball with the leading edge, while having your upper arm securely connected to your chest.
give it a try.
a side point - Oscar mentioned that the pressure point on the hand being the base knuckle of the thumb.... I don't quite buy that for my self... that area is pretty weak (you can't really lift the racket upwards with that knuckle)... by using the middle section of the middle and ring fingers, you will feel tremendous extra RHS added to the upper/side cut action.
we all know how tricky it is to time the 1hbh... and to be honest i have not found 1 clip on the public domain that i really like..... everybody ignores the elephant in the room - the high ball..... every demo is made with balls below waist..
with the method i laid out above, you get 2 extra power sources to deal with the tricky timing, 1 is the connection to your chest, so you get support from the core.... the other is the middle section of the middle/ring fingers which give you an emergency lift...
look at the pros today, they all release the wrist (supination).. in order to do that you HAVE TO swing around (instead of forward), and you have to have strong support from the BOTTOM of the grip.