@KiwiPlantGuy ,
might be simpler on your nerves to place plant back into a colander and
ground grow.
You can take 4 concrete blocks place on ground, and put a layer of coarse
bonsai mix, rest the colander on top, fill in side to just over the plastic
colander, to protect from UV.
Then, if needed a thin mulch of leaves.
Or as I believe the Australian and Americans do, just place on the ground
and let the roots escape at the base. The colander will still air prune
and keep your plant efficient as feeder roots go.
Anyhow, unless a tree / shrub is known for thickening in a pot, not much will
happen in a grow pot.
The over sized pot is for refinement of branches and leaves.
How thick do you envision the trunk to be -------- diameter ?
You can place 6 branches, and grow out problematic bulges etc.
Can you draw or photograph, print and trace to get an idea of what you
hope to achieve?
It will still take 3 to 5 years for the refinement part, by the way.
Think of it this way.
Ground grow for trunk / root and 6 branches.
Oversized container for refinement ------- branchlets
Ignore blooms.
Best of growing.
Good Day
Anthony