Well, I'm with MegAlfOCon on the getting a surgeon who will really listen. One can have an infection without the incision looking like it, one can have issues with scar tissue in places or one could have the pressure set wrong, just to name a few possibilities. I'm only experienced in the pressure issues - if changing position really makes a huge difference, that could be part of it. But you've written where position was better being upright and a different post about lying down being better. For DD even at her best setting, she can under AND over drain (throw in a cold/flu and it can be an almost certain stay in the hospital). Lying down helps when over draining (for chronic over draining the setting gets put up a notch), sitting up helps when under draining (for chronic under draining, setting gets put down a notch). Wash, rinse, repeat until one finds an ok setting. When we could not find a good setting, we've been in very low pressure situation without an antisiphon, later it changed to high pressure needing an antisiphon and even later where the antisiphon wasn't enough. Most people just need an antisiphon and I didn't think most people shunted as an adult get the freaky pressure/compliance problems little kids sometimes have.
If you have consistent positioning issues, tell them and ask if your valve needs to be adjusted. I would also consider asking them to do a shunt tap or lumbar puncture to test the csf for infection and whatever read on the pressure they can do (those are not the best pressure readings but ...).