Like hell it's a myth. 2 blade fixed heads can and will "fight" your fletchings. I have been an archer for well over 40 years, and have seen it many more times than I can remember. Now granted I didn't think about the spine issue but I know full well it is NOT a spine issue because he is having this problem at 40 yards. At 20 yards an improperly tuned bow or improperly spined arrow may have a little forgiveness with a field tip and group well but NOT at 40. If he is grouping well at 40 with the field tip then he will group well with the broadhead if he is not having a STEERING problem! It's simple as that. Tuning your 2 blade to fit well into the helical of your fletchings will 90% of the time solve this issue. The other 10% of the time it is usually because you are "under fletched" and probably need to go up an inch or get a higher profile wing. Those Bloodrunners aren't long enough to really throw off FOC so it would have been highly doubtful if it was that.

Now speaking of fletch (and why does friggin spell check underline fletch?) that could also very well be the issue. He may very well not have enough angle on them. Some people try to get away with a little 1.5 to 2 degree offset (basically straight) on their fletching and that just will not cut it for most fixed blade set up's. It's fine and dandy for a field tip but not so good for a fixed.