another simple grafting question

Is it better to field graft where diameters of scion/rootstock are the same or place the graft lower even if the rootstock is larger.   How high would you consider the max, 3, 4, 5 ft?
Going to graft persimmon,  last year I grafted to limbs because the diameters were similar but now some are not going to work out like I want

The most common grafting techniques need the same diameter. This is especially the case with the newer grafting tools, like the omega grafting tool.

There are however many other techniques requiring a smaller scion than rootstock diameter.

As you now seem to master the principles of grafting with one technique, it is really easy to learn new ones. Just search for images for "grafting techniques", you will find many suited ones. https://duckduckgo.com/?t=ffab&q=grafting+techniques&iax=images&ia=images

Having grafted many things, but not yet persimmon, I cannot tell you what works well for persimmon, but you can specify that in your search, most techniques seem to have been used.
https://duckduckgo.com/?q=persimmon+grafting&t=ffab&iar=images&iax=images&ia=images