We do not know where your bare shafts are landing with respect to your fletched arrows; you only state that your bare shafts are "...hitting a little low and just barely to the weak side."
Also, it helps to know the distance you are testing at, I mention this because you're shooting in the basement.
I have found what seemed "good results" at 10, 15 yards turned out not so good at 20 & 25 yards.
Too close = not enough distance for fletched arrow/bare shaft discrepancies to appear.
I also recommend to test at farther distances and do so a number of different times, this will confirm your test results. Dang hard to put the carbon back on the shaft once cut...
As I understand it, the fletched arrows tend to go where pointed, thus this is one's reference point to which they tune the bare shafts. Emphasis on "where pointed"; sometimes not the same as where we think they're aimed :eek: )
Good luck with your testing, it is a thrill to see a bare shaft travel 20, 25 yards and stick dead-on, straight into the target