I wish I had a good answer. Here are some of my statistics from bark grafting in the field:
2012 - My first year of bark grafting. I grafted 9 native male trees in the 2" to 6" diameter range with scions from a prolific local female tree. All trees accepted scions and grew vigorously.
2013 - We had a huge cicada crop. Ass of my grafted trees as well as native trees were hit hard. I grafted a lot of native male trees that spring with native female scions but they all failed because of cicada damage most likely. Someone sent me a prok and a 100-45 scion that I grafted later than the rest. They had no leaves when the cicadas were abundant and when they leafed out, they had no damage. These two trees survived. Growth was good but not as vigorous as the native trees the previous year.
2014 - I grafted 49 scions to 23 trees most in the 1" to 6" diameter class with a few smaller. 34 scions took on 22 trees. These scions were a mix of named varieties I bought from Cliff England, and scions from native and named trees from across the country I traded with others. None were Kaki. The only tree that failed, failed because an animal knocked out the scion.
2015 - I grafted 40 trees with 40 scions. Only one was a larger diameter tree grafted with multiple scions. Most were in the 1/2" to 1 1/2" diameter class. The scions came from trees grafted the previous year that had not produced fruit yet of course. Only 10 trees accepted scions. I will also say that this was a very odd year for my native persimmons. They leafed out very late, the leaves were smaller than normal, and they appear to be battling something. Regular producers were late to bloom with very few flowers that lasted a short time. I have yet to see persimmons forming on my native trees but with this weird year it may be too early. The Prok and 100-45 are in their third leaf. Both flowered and the Prok has 2 small persimmons on it.
Some years with some trees, when I cut down a persimmon to bark graft it, it is like I just cut someone's arm off. It just spurts out sap like blood. Other years with other trees when I peel back the bark it is green but not particularly moist.
Rootstock condition due to weather, insects, timing, etc., graft union quality, scion vigor, compatibility, 60 vs. 90 chromosomes, who knows. I'm sure they all play a role. There are lots of variables. We can probably improve graft union quality. I found pressure is key and I like electrical tape for that. I've learned that liquid sealants can leak into the graft and destroy the contact. Parafilm-M does a great job of keeping the scions from drying out giving it time to bond. We can probably improve scion vigor by more careful selection of scions. We may be able to improve timing a bit but we are always at the mercy of mother nature...