Attempting to align merger/splitter in a belt system that is raise can be a bit of a faff, mostly because you have to try place the belt first then split/merge in the middle of it.
It's a real struggle to align things when you are forced to use belts and try manually align along the belt, my thinking is that if you could place the merge/split on to a belt raiser, then bring the belt to the merge/split after it's placed, things would be a lot smoother.