After some thinking and correlation, I came to believe that a proper arrow is at least as important as the bow efficiency.
I mean not only weight and drag (diameter & fletching size).
Achieving greatest distances with a heavy arrow, as described, got me thinking.
And then I remembered my amateur rocketry times.
Those rockets usually look like short, fat arrows, but the ballistics are essentially the same, at least after burn-out.
And the magic parameter is the CoG - CoP distance, as it's usually called in rocketry.
CoG is the center of gravity (i.e. the centroid).
And Cop is the Center of Pressure, i.e. the point on the longitudinal axis where the aerodynamic forces equal out.
The CoG must be in front of the CoP, else the projectile is unstable.
CoG and CoP at one point would be meta-stable, i.e. the thing continues to fly on in any orientation you disturb it.
The distance between both points is a kind of "lever" the gravity and drag forces act on the projectile.
The larger the distance, the more stable, but the greater the "pull" of gravity on the tip.
The FOC is similar, but describes the centroid position in relation to the geometrical middle.
You can observe this effect on child "shooting" toys sometimes - if you shoot the fat, lightweight (foamed) projectiles angled upward, they just stop on apogee and drop down like dead. No pointing downward.
To come to the point - for flight shooting, you need a small CoP/CoG distance.
That means, small fletchings (which pull the CoP backward) and small tip weight (which pulls CoG forward).
And those properties seemed to be matched best with this old, heavy carbon arrow of mine.
But you need low wind, and a good technique, as the flight is less stable.
Not coincidentally, the Turkish flight arrows are like that.
Arrow tuning should have the most significant effect for traditionally style (Korean) bows.
Nothing really new, just a recap in more technical terms ...