I don't think enough antigen tests are being reported to really effect positivity rate much. Antigen tests only make up about 2% of reported testing.
Iowa has said they added 1000 positive antigen tests in last week, I've never found a county break down. It is why Ames suddenly spiked to a 69% positive rate. In fact, Iowa's officials said some counties may appear to have over a 100% positive rate because of this. 1000 is approximately 2% of the total positives not a daily positive. Add 2% total of 6 months+ of test in a few days and it really gives you false data for a time. Clearly levels in the college towns are higher and somewhat disproportionately higher than the population increase. But not the high levels it initially appeared. By Sunday the 7 day average should more reflect what is happening in Ames/Iowa City.