It may require some trial and error adjusting the dial on the flapper and observing the results over a few days.
Strategy 1. Adjust the dial so the maximum amount of water is left behind in the tank when the flapper closes but the toilet still flushes reliably.
Strategy 2. Put some food coloring in the bowl. Adjust the dial so the coloring is consistently eliminated during the flush.
(One morning on WRKO Radio) The tub's not clean! Let's remodel the bathroom.
(One afternoon on WRKO Radio) It's time for an oil change. I'm going to trade in the car for next year's model.