Rolling the hightest number isn't an instant win is it or can't you go above the max roll. If not I was facing the boss of the collage, I had a plus one to my roll, we both rolled a 6 it was her win.
As Krellen says, you can't go higher than the number of sides on your dice. Also, draws will always count as a loss to the attacker (never to the defender) and in CLASH a draw means that neither person gets to use their abilities :)