I will make a video tonight of the cleaning side of the tool and post it tomarrow. If yours isn't like mine as far as how the water flows then I would take it apart, check for built up hair in the cleaning head, then. Look for any problems with that small plastic tube that goes from the trigger to the spray bar.
Mine doesn't clean real well in the middle if the water pressure to too high. 200- 300psi ish is great. I'm sure differant machines flow water at different rates, you might have to play with pressures and the flow valve.
I didn't look but does the flow valve have a packing nut you can tighten to help keep the know from turning so easily?
If it does, tighten it some if your having issues with it moving.
As far as flowing differantly once you get it hooked up, it always will as hot water acts thinner and will flow more once it gets to the head, if you have a temp setting turn it down some, high temps can actually damage some upholsterys. Just remember your not loosing any heat threw the air like a spray jet, it doesn't spray, the small holes just fill the spray bar, tool should be adjusted so it just penetrates the fiber. So you also don't need a lot of pressure.
Hope this helps. I am not paid or reimbursed for anything I've said here, I do however love this tool. And have used it since it originally came out.