Not doubting your ability to watch the flight of an arrow, but for me...I have never trusted my evaluations of an arrow in flight, call me a skeptic. To prove to myself that the arrow is doing this or that in flight I usually combine group tuning of bare and fletched shafts with shooting bare shafts through paper.
If I am looking at the arrow in flight, I probably did not make the best shot I could have because I was trying to watch the arrow. So if I can concentrate on paper and punch holes I can convince myself of what is happening in flight. Then combine that with the information from the group based tuning and I am confident that I have enough information to make adjustments. I also have a hard time putting any stock in how the arrow is sticking out of the target, just too many variables (unless it is extreme).