I think that you have to direct more energy into the top. This way it will only grow there. But I am no expert...
Discussion
And maybe alot of food for the tree.
Yes it get fertilized regularly. Looks healthy, its just the shape thats not right.
i know when i've grown cannabis, you can nip out the leader and it forms a 4-way, so to resume one to be the leader you have to cut the other 3.
it's always gonna have a kink where this all happened but it should start to ascend more if it's not dividing the top growth between 4.
I think you may be right, I believe if you start to trim back the lower branches, it will start to stimulate growth towards the top