That has got to be the stupidest logic I ever saw. If my aunt had a set on her she would be my uncle.
First of all, when the riders went to the gate they knew the race was a mile, not a mile an eigth, and they rode accordingly!!! Do you really think Prado woulda sped like that if he knew they had another eigth to run? Of course not. Also the training of the horses for that race was for a MILE!!! Workouts and gallops woulda been modified.
To use the finish of a race at a different distance and say soemthing like that makes absolutely no sense at all, as conditions in a longer race would have been totally different.