Frazier was taller and had a longer reach than Tyson.

You really have to wonder who would back down first between these guys both of whom were face first fighters that would stalk down their opponent.

Frazier even when being beaten had impressive head movement always up and down with very slight side to side weaving and gloves up ready to unleash Hell. When Tyson was in dire straights he stopped moving so much, he would throw 1 punch at a time. When Frazier worked his way in you were going to pay the price, Tyson was easier to tie up IMO.