There are a lot of variables that affect how big the gap is between the last line of text and the page number in the reading footer, and patching adds more, but I can put them into three main groups:
1. The size of the footer itself. Unless you use the FullScreenReading feature setting to remove it altogether then the only way to change its size is with the `Custom reading footer style` patch.
2. The font size and line spacing settings, and also in some cases the choice of font itself. These are set by the adjustment sliders on the device, but can also be affected or overridden by the book's stylesheets.
3. The page margins set in the book's stylesheets, which can be set by the publisher via @page in the CSS stylesheet, but for some books also in the Adobe XPGT (page-template.xpgt) stylesheet.
You might want to try sideloading this
margintest.epub book to work out what is contributing to the gap. This book has no added margins, on the first page it draws a rectangle that shows the area normally available for text, and on the following pages is some sample text.
1. If the gap between the bottom of the rectangle and the page number is larger than you want, then you need to alter the options in the `Custom reading footer style` patch to make the footer smaller, and if you want to make it very small you might also need to reduce the font size used for the footer.
2. If the gap between the rectangle and the page number is okay, but the sample text on the following pages doesn't reach to where the bottom of the rectangle was, then it is simply your font size and line spacing settings that are to blame. I.e. there is not enough room for another line of text to fill the gap, so all you can do is adjust the font size and/or line spacing to change that.
3. If the sample text in the margintest.epub book is close to the page number but not the text in other books, then the problem is that the other books contain added page margins. You can remove the margins before sideloading, the Modify ePub Calibre plugin is useful for this as it can remove the page margins from the page-template.xpgt stylesheet too. Or else you can investigae the `ePub fixed/adjustable top/bottom margins` patch which can override the @page margins set in the book's CSS stylesheet, and the `Ignore ePub book Adobe XPGT stylesheet (page-template.xpgt)` patch which causes the book's XPGT stylesheet to be ignored.