There are some intangibles at work there.
Would the team down one point with a minute to play succeed in getting into FG range because it will play with abandon, or will it choke under the pressure and not even make a first down, maybe turn the ball over? Would that same team playing under the less desperate circumstances of a tie move the ball right down the field into FG range, or even score a TD?
Would the team with the lead play prevent defense, risking giving up too much yardage but preventing a big play, or go all-out to force a turnover on downs, thereby risking a big play? Or would that same team in a tie situation take for granted that the other team is just going to let the clock run, and thereby get caught napping?