What type of service?
20k a year ...probably all of it at whatever level of filtration it provides. You're not loading a filter too much with that type of driving. Hardly any sizable percentage of high combustion byproduct production. It's the cleanest service you can imagine. It would be the same for an equal amount of fuel, as integrated in mileage, for something like a taxi ..which also experiences very little warm up combustion byproduct production. It has the disadvantage of having mileage be a very poor metric for determining fatigue of both oil and filters.
OTOH, drive 3k in 6months as a daily driver??? That's a different story. There mileage can't account for the "use". If the mileage is low enough, then the capacity/tolerance can still make it without loss of functionality.