You will hear me talk about FOC, but to be honest I think it is about the least important factor in arrow flight. The only thing that is important is that you have enough. 9% with adequate fletching on a hunting arrow should work fine. It just forces your fletchings to do thier job is all. Less FOC is a bit harder to tune, but it can be done. Too little FOC and the front of your arrow will try and wander around and with fixed blades the blades will try and steer the arrow instead fo the fletching. I have used as little 7% with small fixed blades they flew well out to 40 yards. I shoot feathers though. It just depends on how good your set up is. Bob Ragsdale thinks it is a bunch of crap and doesn't even concern himself with it from what I can tell.
Butch, I don't think you fully understand what the bares shaft test is and what it tells you. The test you did probably didn't tell you much at all. For starters a bare shaft is very sensitive to form and arrow variations. You should test with really good arrows and more than one. Not a junk arrow that you don't want any more. Chances are that arrow is crap and that's why it didn't fly right. Also you have to shoot more than once. It is process, not a test per say. And I'm confused by your statements. I don't think you did the test correctly to begin with.
You really should have started at 10 yards, it's less scary when the arrow does crazy things like it did with the 100 grn tip. You said the arrow with the 125 tip hit fairly straight but the bottom of the target? Where you aiming at the bottom of the target? The object is to get the bare shafts hitting the same place as the fletched ones and fairly straight. Just like the broad head tuning method. I don't think this is what you were doing? If you get them to group together and the rest is way off from what you think it should be or the arrows are not straight in the target then you most likely have a spine problem or your form is off. I actually like them a bit nock high myself.
What the test you did shows me is that your set up is no where near as good as it could be. And that your fletchings are doing a great job of correcting your arrow flight. Technically the 100 grn should have flown a bit better because it was a stiffer arrow. However you were broad head tuning with the 125 tips so it is set up for the 125 tips. If you change a dynamic on the arrow it will affect how it flies. You would have to re-tune the rest for the changes you made in most cases. The fact that 25 grn less tip weight had that big of an impact though really makes me think your arrows are weak. I think if you had a stiffer arrow the difference would not have been that great. You saw what it did with now fletchings and the 100 grn tip. Imagine what it's doing with the 100 grn broad head on there and how hard the fletchings are having to work to keep it straight. That is why you should not shoot a different weight hunting tip as your practice tip.
That being said, I wouldn't mess with it this close to deer season. I would just go with what you have since you are comfortable with it and it seems to work. You are probably still tuned better than most hunters out there. If you want to play with it wait until next spring when you have more time to dink with it and there is no pressure to rush it.
I will also add that just because you get your bow to bare shaft perfect does not mean your broad heads will still impact exactly the same place as your field tips. It will tell you that your arrows are coming out as straight as they can be though. Broad heads are not the same as field tips so it should not be a shock that they fly slighty different. You could either compensate with your sights or tune your bow to shoot the broad heads in the same place as your field points. It should be pretty darn close to begin with so only very slight adjustments would have to be made.
Check out this link, it is a thread about tuning on AT. One guy describes how he bareshaft tunes, and I describe how I do it. I don't really care for using paper myself. They are two completely different tests and shouldn't be mixed in my opinion. I also list links to Eastons Tuning Guide and Bob Ragsdale's home page farther down the page in that thread. We have talked about it here as well if you search for it. Use the key word "bareshaft" or "bare shaft".
tuning thread
I don't want you to think I am arguing with you or being an ass either. I am just letting you know how I am interpreting things from the way you are describing them.
Good luck,
Paul