the only reason i say about a foot from the turbo is that way it's a good reading. you do want it after the turbo though, and at the most concentrated part. it doesn't matter which way it faces(up or down) but being on top does make it easier. if it's on the bottom it might just make it harder to get to that one nut on the bottom of the downpipe. also the less time you have to spend underneath the car makes everything easier and safer.