The times I've bare shafted fox, I began at 5 or 6 yards and tuned, and then was able to move back a bit, and fine tuned, and just gradually extended my range while tuning until I was out to 25 or so yards with decent flight. I did learn enough to know that I prefer to rough-tune a fletched arrow and proceed afterwards and strip off the feathers to do the more sensitive bare shaft test. In mind, bare shaft testing is just too sensitive to use before any initial tuning.
There are a lot of bare shaft tuners on here who will chime in sooner or later though. I'm sure they'll tell you everything you need to know about it.