According to weather reports, Midland received just under 5 inches of rain over a 8 hour period...3 inches less than the Tawas area, however, Midland was hit just a couple of days earlier with another 2 inch rainfall in a 2 hour period...which saturated the ground enough that that caused a much larger runoff with the bigger storm that contributed to the high water levels in the Wixom and Sanford contributories.
https://www.clickondetroit.com/weather/2020/05/20/major-flooding-in-mid-michigan-how-much-rain-fell-how-historic-was-it/