What’s the light source for this tree? Being that it’s 20 years old, needs support to stand on it’s own and is rather small, I’d be included to think it doesn’t get much light and grows very slowly.

Getting the tree to look great is going to take a while, but you can tidy it up.

Id personally start with removing all of the growth at the bottom and pitching back the very tips of branches at the top. I would do this as close to summer solstice as possible. The longer day lengths equal more enthusiastic back budding.

or, if you wanted more of bush look, removing all of the top portion is also possible, though, that’s looks to be the only are that gets any light. Neither of these options will kill the tree.

How long has it been since the last repot? Ie bare rooting, root pruning and untangling and a complete change of soil?

I would cut nothing yet. If you see any old, dead growth remove it. But the tree has great character, it looks healthy, and like you said, it fits the space.

It goes for most trees, best to prune them starting at a young age to keep them in check. It doesn't actually look bad. Was the bottom braided?