Why are you doing runups?
Runups are done for different reasons in different aircraft at different times of the day.
Frankly, runups are not very important for a fixed pitch C172. You can tell if the mags are working pretty much at idle and at 1600 static rpm (or whatever) the engine is not making much power, so its not testing the mags under load. Largely its a practice carried over from Tiger Moths. (come in Jaba)
On a cold day, runups in a turbocharged twin are a prolonged affair. I'm warming the oil, checking fuel pressure, vacuum, prop governors, feathering accumulators, alternators.
On difficult runways, in fixed pitch aircraft, I've done mag checks during the take-off run.
Do runups for a purpose you have thought about - not as a robot by rote.