The calculation of green dot is a bit rubbery at best.
A320 2 x Wt plus 80 or 1.5 x wt plus 110 for the A321 (plus altitude adjusts.) Hardly a figures to hang your hat on. Then you have to consider an acceleration in most cases to exit the hold at 250 kts; and how to achieve that efficiently. And what of performance factors for individual airframes. Does this influence the speeds?
All very theoretical and not necessarily practical in the real world