Click n Ship question

Due to the madness of the Asylum I have now received and shipped a good number of boxes. I use Click n Ship most of the time to print labels and pay for postage. I have received some odd sized boxes in the past such as shoe boxes, smaller than medium but still cube shaped boxes, non-priority plain Jane brown boxes, and an assortment of other random sizes/styles, all of which have the Click n Ship labels on them. However, when I use Click n Ship I see no options for anything but the "regular" priority boxes. Does anyone have insight on this?

Thanks in advance!