I would say that he has mastered it (or is very good at it).
How many games has Utah been favored in during the Bronco-Whit era? 3?
Also, the fact that BYU needed dramatic plays to win in 2006, 2007, and 2009 lend credence to this idea. These BYU teams were vastly superior to Utah, yet barely won.
Kyle has his faults (he relies too much on emotion, is too conservative with the lead, loses many games he shouldn't), but I don't think a reasonable argument can be made that he isn't much better coaching the rivalry game than Bronco is (and IMO, he indeed has mastered it).