It doesn't work that way; they have to offer the same (lowest) rates to all political candidates. I know this firsthand; I have placed buys for some state legislative campaigns during the last three cycles. And the article is correct - buying non-preemptible time in September is ridiculous.
I too am familiar with media buying and the lowest unit rate rule for political advertising. You are correct, of course.
Bending the topic a tad, the chart indicates the dominance of WBNS over WCMH is rather remarkable. If the rates reflect the Nielsens number, channel 10 must have a substantial viewership advantage over channel 4 in that market.