From the screenshot that I see, you must be using a rather ancient version of PTXprint, as the available settings on the Tabs+Borders page changed significantly quite a while ago:

You will notice that in the newer interface, you can select different kinds of borders - either at (dynamic) text border, or a PDF border (Legacy) which is static and doesn't change size according to the amount of text on the page.
It might also be worth looking in your Advanced settings' ptxprint-mods.tex file to see if you somehow enabled it there (again, a LONG time ago before the user interface was even built for this feature).
I recommend downloading and using 2.8.22 which is available from here: software.sil.org/ptxprint/download/