There's only two adjustments:
1. Where the straps pass through the buggy.
2. Where the bungee that wraps around the neck fastens.
If you tilt the bass sideways to where the neck lies comfortably against your shoulder, the place where the lower bout contacts the floor is where the buggy should be placed. Simply adjust the length of the strap between endpin and buggy so that happens. Doesn't have to be exact.
If you wan't to have the bass trail behind you when you walk, you may have to position it higher up the bout. Again, just lift the neck until it's in your desired traveling position, see where the bass touches the floor and put the buggy there.
Or position it between the two points if you want to use both configurations. There's plenty of wiggle room.
For the neck strap bungee fastener, you're positioning it to set the tension of the bungee. Too low down and the bungee may not reach around the neck, or be stretched too tight. Too far up and it will not be tight enough to keep the buggy in position.
Lastly, the straps do not slide easily through the slots, which is good, otherwise you'd be constantly readjusting them. What I find works best is to both push and pull the straps through the slots at the same time. Push from the side you want to shorten, pull from the side you want to lengthen.
Is that sort of what you're looking for?