Update #2.
75% of the peach on peach grafts took and the branch grown off these buds have had growth that I didn’t foresee. Each are 2-3 ft long and 1/2 inch thick. I wonder if this crazy growth has to do with too much nitrogen in fertilizer Here is three of them - will need prune off all but one
I guess it doesn’t have to be perfect fit as long as (a) knife is sanitized properly and (b) some portion of cambium is in touch and (c) you wrap it around with Parafilm or such to ensure no moisture loss. I am sure winter weather, zone, rootstock, etc all play a role