Looking at some details about the official Raspberry Pi screen, this seems to be a limitation of the display for technical reasons.
However, there is a trick you can do to nudge the window so you can change the font DPI, which may be your only hope:
Some windows in X are cut off at the side/bottom of the screen?
This is unfortunately a side-effect of many developers assuming a minimum screen resolution of 1024x768 pixels. You can usually reveal hidden buttons and fields by;
- right clicking on the edge or top of the window,
- picking "move"
- using the up arrow key to nudge the window up off the top of the screen