Good post.
If someone is having an issue with an injection site it also could be from hitting the same pin location time and time again. You would be surprised if you took a sharpie and marked the locations how we go right for the same exact spot. Back in the day I used to do this to try to stop scare tissue build up, once you get a decent amount of that going it can ruin the site completely. I have a few spot I cant shoot because it wont inject out of the syringe.