I’ve been doing a lot of dry fire during the current ammo shortage, including playing around with different techniques. I’ve learned that a high thumb grip—my thumb resting North of the cylinder latch gives me better results dry fire than my normal low thumb grip—thumb pointing South.
I have tried it out live fire yet, but I was wondering what the consensus is regarding high thumb versus low thumb—this is with a J frame Smith. 
Funny you should ask. I was recently experimenting with it. I seem to favor the low thumb at this point, but I am still messing around with it.
Low for me, all revolvers, that said do you change it when shooting one handed & two handed. I do when using a semiauto.
I’m concerned about using the high thumb. Our revolver cylinders are just short enough for the tips of my thumb, & the Boss’ thumbs to be at the front of the cylinder. I do like my thumbs, so I’m going to keep using the low thumb grip
My thumb ain’t long enough to come anywhere near the forward cylinder gap.
It doesn’t even encrouch on the rear gap.
The cylinder latch acts like a thumbrest for me using the high thumb grip, which maybe is why the barrel stays "solid’
I honestly was surprised with the Boss’ gun I don’t know how she did it, but I caught it before she lit her nail polish on fire
IMO, it sounds like you have a trigger finger placement issue that you are trying to cure with a support hand placement change. If the sights are moving when you pull the trigger during dry fire, try changing the placement of your trigger finger (and corresponding grip) so that there is little to no movement during trigger pull. Then, re-evaluate your support hand grip.
I switched my stock grips with wider pachmayr’s that allowed for a higher hold and pretty much puts my trigger finger naturally where it needs to be.
I should have mentioned this was shooting with one hand, not supported.