Jayan cutting back the tree's root system is directly why your tree has not put forth vegetative growth. Now you want to cut back the vegetative growth, which on a small tree will again reduce root growth. A tree is a unit, cutting one portion affects the entire tree. What your particular tree needs is to be left alone, and given proper nutrition, climate, and care that it deserves.

Kumquats are bushes and need to put on water sprouts.

Steve

I would say too, just give it time outside. Keep it fed and watered. With sun it should put out more growths along the trunk and inner branches. The more new growth it puts out, the thicker the trunk will become. Eventually it will stand on its own.

Jayan the combination of wind, July temperature, and radiant heat from the brick may be factors. To mimic spring growth you need to mimic cooler more pleasant weather with more shade and a wind break.Kumquat trees don't require pruning except to remove suckers. If you want to prune the best time is after harvest and before the next flower.

I wouldn't know about that

Is it OK to tip prune water sprouts when they get 'too long'?

I think I'm beginning to change my soil

you are slowly killing your trees with kindness they need some time to recover

It is through water sprouts that every citrus tree of mine has increased in size and productivity. I don't trim my tree's "production" sprouts.

Steve

I think I'm starting to change my soil structure