When I load test_cropped.pdf on my Sony, there aren't really any margins on the top or the bottom—or least the margins don't appear any larger than they do in a PDF reader (I tested on evince on linux). There do
appear to be margins on the sides, but presumably this is just a result of the fact that the proportions of the cropped page don’t match the proportions of the reader’s screen. (I.e., it can't zoom in any more horizontally while keeping the page on the screen vertically.)
My firmware is 1.1.00.18040. My reader is about a year and a half old. I can’t believe that’s the difference, though.
Personally, I find that page to be readable if you put the reader in landscape mode.
For this particular PDF, I would have used
soPDF rather than BRISS, mainly because there would be no need to manually select the crop region. Probably the results would not be much different. But if you don't need searchability or dictionary features, however, you could try feeding it through
PDFLRF instead (or in addition). That deals with proportion mismatches in a different way (i.e., dividing up the page into as many chunks as necessary to maximize the width, combining the bottom of one page with the top of another if need be).