WHY DO YOU THINK A 20K TIME CAN BE CONVERTED TO A MARATHON USING CALCULATIONS????
Canova has his athletes do upwards of 40k in hard training before he can tell what kind of time his athletes can run. This is one of the dumbest things about training in America. We say "hey what will it take for me to run a 2:10 marathon? ...oh, says here I have to run x time for a 5k and then if I do this calculation right I'll run 2:10."
STOP USING FORMULAS TO PREDICT MARATHON TIMES.