Okay, I resolved the problem. Apparently it is because at the end of my row groupings I had inserted a row grouping that didn't really group on anything, but...
It seems that despite making the list object 11x8.5 and checking the box to create a page break after the list item, it just takes a whole lot of tweaking...
It looks like I just needed to change the page size in Reporting Services (in Report Properties>Layout) and then do lots of trial and error with margins and on the...