The problem that you have is that, since recent versions of gnome (3.14 maybe), on startup (and resume from suspend, as well) gnome sets the DPI to 96, whatever the real DPI is (which X has always guessed correctly).
That unfortunate design decision with gnome, that does not appear to be justified by HiDPI support (because HiDPI works equally well without that forced DPI setting), forces us to go to the trouble of manually setting the DPI each time (after each reboot or resume).
Say that your true DPI is 185 (as you can determine from Xorg log), if you open a terminal window and do:
# xrandr --dpi 185
Then 100% in evince and other programs will be the true size (or a very good approximation).