Well done, Revolverman! I like your persistence.
I was not satisfied with the Walmart/Stearn ATV seat cover because I was still sliding forward more than I liked, particularly when riding downhill. My solution was to seek out a local motorcycle seat upholstery shop. The guy I found made the seat slightly wider and much less "concave" for only $70. For a skilled upholsterer it is a very simple job. The maximum height is now 6" (above the "A" in CAROLINA) and the max width is about 11" (above the "C" in CAROLINA).