Why would you tune something where the end result is already what you are obtaining. The goal is to have BH and FO impact the same. You've reached that, there is nothing more to do.
I would tend to agree. I guess the "real test" though would be to take a broadhead with alot of exposed blade area...and shoot it to see if it groups with your field points. If they do impact the same then I guess you could say the bow is tuned....
...unless you found a broadhead with even more surface area and then attempted to see if that broadhead grouped with your fieldpoints.
In my opinion that is redundant. Your broadheads hit with your fieldpionts. Destination reached.