Just because you know the parts is supposed to 90-95% full does not mean you are actually practicing it. In a recent on-site training session the participants all understood the importance of molding a part short during 1st Stage Injection, but learned an important lesson in the lab.
Situation: In lab, we were establishing the first stage fill. We made a part which was just full and weighed the shot. In increasing the transfer position, they made a part which they thought was 90-95% full and weighed it. It turned out to be 98.5% full. They were amazed and learned a valuable lesson about why it is important to measure the parts and not just assume. The lesson is, you must practice what you learned so that you understand the application.