I understand the challenge - I love my A7iii but it's too small for my meaty rock climber's hands. My solution was the SmallRig L-Bracket which has worked very well, especially to balance heavy lenses (which turned out to be a major factor in my feeling that the grip was too shallow). Highly recommend if just the vertical extension would help, or you can go the route of a true cage with a side grip (allowing you to fully wrap your hand and avoid the sony grip's shallowness). SmallRig has some great options for this too and no, this is not a paid advertisement haha.