Keep in mind,the 30%plus FOC that Ashby is using requires less fletch.He isn't advocating it on normal FOC arrows.Personally,if I were shooting those point weights,I'd use three 5" or four 4".Things can look great till you get shooting broadheads in a variety of hunting conditions etc and you may need more stability.
I'm using a fairly small,3",four fletch but the arrows are 32%-35% FOC.I've tested them in all conditions,including high cross winds and they are stale.Ashby uses that fletch in specific circumstances and fine tunes the size on each setup with a pretty stringent tuning regimen.