Brod
I would have said exactly what Michael said. The tree needs a lot of feeding and room for the roots to grow strong and thick. It greatly assists with taper. A good draining mix. The problem with that is obviously that Swamps like water, so the poly container will have to go into another container which holds a couple of inches/centimetres of water permanently. With the constant water source, the roots will also grow strong towards it. The Nebari is improved and so will the taper.
I'm not convinced to cut too much on it. Not my tree and Michael clearly knows a lot about Swamps as it is his favourite species. But, if you give it room for its roots to grow, water, fertilizer; then I would imagine you need to just let it get on with developing that taper. Limiting to top growth will influence how rapidly the roots develop. I do however agree, when the new growth comes, carefully start selecting your branches, remove the rest. Perceptually, to the eye, the tree will already have an improved taper, by cutting at the point Michael has proposed. If that is the way you are going, then allow the tree to get on with it after that. Again, choosing the main branches you want to keep.
Curve ball, remember the top of the tree can also be a sacrifice branch, it does not have to go early on. The top of the tree growing strongly in a swamp does help the rest of the tree to develop.
I will probably over the next few weeks be posting my photos for some ideas and advice on my swamps. I find it a challenging species, until you get that one which is absolutely spectacular. Good luck.