slideshow_img_size_across_two_lines
At the bottom of slideshow pages (per-image HTML pages), links to different
sizes of the image are listed (e.g. "reduced", "large", "original") with
the sizes of the files if
print_img_size_on_slideshow
is set (which is
the default). When these links are listed with their sizes, if
slideshow_img_size_across_two_lines
is set, the
file size is on a seperate line from the file type ("large" et al).
Vertical space is a precious commodity, and links to image variants come before any image description—the result is that people may have to scroll down to see the image description. The default layout is to have the file type ("large") on one line and the file size ("375k") on the second; this uses one more line of veritcal space than strictly necessary. Setting this to 0 will give you links like "Large 375k".