Watched a kid fail a 6G test 4 times in 2 weeks, then a 30 year hand from Gary showed him one grip change
This apprentice at our shop in Gary was capping out on his 6G root, 4 tries in 2 weeks, all of them leaking on the bottom side. An old hand named Ray watched him for maybe 2 minutes and told him to stop rolling his wrist and walk the cup instead. Next pass, clean root, first try. Ray said he'd been letting the rod angle drift about 4 degrees without knowing it, so what grip change actually fixed your root passes when nothing else worked?
Did you ever try changing your body position instead of just your hand? I had the same problem on 6G pipe for weeks, kept getting that bottom side leak, and what finally fixed it was dropping my elbow down about an inch so the rod angle stayed ahead of the puddle instead of behind it. That tiny shift kept me from dragging slag into the root, and my passes cleaned up that same day. Sometimes it's not the grip at all, it's where your whole arm is sitting relative to the joint.