@JSWolf,
@Semwize is correct. I hadn't realised until now what 'ReadingFooter' property 'qproperty-footerMargin' was actually used for.
It's the width of the right & left corner tap zone blocks in the footer which can be used for turning pages. Whereas if you tap the caption area you bring up the scrubber.
The caption area is the area between these 2 corner zones so, by definition, you can increase the caption width by reducing the width of these corner zones. In theory you could even set them to zero to have the caption use the whole screen width, but I suspect that would mess up the header's top right corner tap zone used to create a dogear bookmark.
It's not necessary to create a new patch (
unless you really want to). Instead you could add @Semwize's Find/Replace lines to either your customised
Reduce new header/footer height or your customised
Custom new header/footer font because both patches are targeting the same bit of nickel CSS (namely ReadingFooter.qss).