not quite responsive

I’m using it on SuperSimple theme. Same dev as Blank Slate. Very minimal css so it shouldn’t have an affect on this plugin. Did a 5 column test page and hit Ctrl+M to test for mobile devices in FF. I get 5 columns or 1.
It would be preferred for it to step down to 4, then 3, then 2, then one column(s) as the width of the page changes per device.