As said in the readme, here my "xrandr --prop" output:
------------
Screen 0: minimum 320 x 200, current 1024 x 768, maximum 1024 x 1024
VGA disconnected (normal left inverted right)
LVDS connected 1024x768+0+0 (normal left inverted right) 0mm x 0mm
        BACKLIGHT: 0 (0x00000000) range:  (0,0)
   1024x768       60.1*+   85.0     75.0     70.1     60.0  
   832x624        74.6  
   800x600        85.1     72.2     75.0     60.3     56.2  
   640x480        85.0     72.8     75.0     59.9  
   720x400        85.0  
   640x400        85.1  
   640x350        85.1  
TV disconnected (normal left inverted right)
        BOTTOM: 37 (0x00000000) range:  (0,100)
        RIGHT: 46 (0x00000000) range:  (0,100)
        TOP: 36 (0x00000000) range:  (0,100)
        LEFT: 54 (0x00000000) range:  (0,100)
                TV_FORMAT: ????
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xorg-server 1.3.0, xf86-video-intel 2.0.0, screen size in mm: 303x228.
I tried to force it in my monitor section with "DisplaySize 303 228" but it did not work. The only way I found to get font DPI fixed was to use "xrandr --fbmm 303x228".