Where should I place grafts on these junipers?

[Esolin]

A few years back I picked up two Blue Point junipers for cheap. The trunks weren't amazing, but they were nice and thick, so I figured they'd be good practice material. I topped them to half height after purchase, hoping to push some backbudding down low, but Blue Points are too apically dominant and they haven't cooperated. Now that I have some kishu and itoigawa mother plants for scions, I'm thinking they will be good grafting practice instead.

My question for someone more experienced with grafting is, can you graft scions in the middle of a large trunk without issues, or is it always best to graft near a branch junction? Would approach grafting be wiser? These junipers have long straight trunks which means for a good composition I'd want to graft low and jin a lot. Here are the trees with locations I'm thinking of grafting marked in yellow. Just wondering what the smarted approach would be, as this will only be my second time grafting. First attempt was 60% successful. (One scion got knocked out of alignment.) Thoughts? Thanks.

 

[Wires_Guy_wires]

I've done trunks and thick branches with the same success rate as finer branches. But since trunks are wider, it makes cutting them in a bit more difficult. The cuts, when placing a knife on fat and wide branches, ends up being crescent and wide, which makes healing more difficult.

So I'm considering to DIY a tiny chisel from a screwdriver so I can make wounds no, or just a bit, larger than the scion.
My wounds look C-shaped now, and I'd like them to be more |_| shaped. I'm thinking to cut the left and right hand side with a knife and shimmy the flap upwards and cutting into the tissue using a chisel.

 

[Shibui]

I've had much lower success with grafts on thick trunks and branches as it much harder to judge where the cambium is relative to a thinner scion. For me, approach grafts on thicker trunks have been much better option as the scions stay alive long enough for the cambium to meet, even if I haven't aligned just right.
No problem grafting in the middle of a trunk section. If you have cambium you can graft. The problem is aligning the scion to match cambium.
With my experience I'd go approach graft on those trees.

 

[Esolin]

Thank you both for the advice. Perhaps I'll try one with scions, and the other with approach graft. Anyone know of a good resource for learning how to approach graft? I understand it in theory, but I wonder how the bottom of the graft is handled once it's time to separate the graft's roots. Seems like it would leave an ugly, hard to heal scar.

 

[Shibui]

but I wonder how the bottom of the graft is handled once it's time to separate the graft's roots. Seems like it would leave an ugly, hard to heal scar.

Depends on the size of the scion but usually cut the base of the scion as close as possible once it is growing well. Then the rapid growth of the scion usually heals the cut pretty quick. All of mine have healed well - better than most of my trident approach grafts for new roots.