Played around a little...
Dont know whats the name of your output is, my monitor is HDMI2, yours is for sure different.
so if you didn't get any further til now you may like to play with this line:
xrandr --output HDMI2 --mode 1024x768 --scale 1.5x1.5 --pos 0x-100
where scale is not neccessary to use and -on my system- I need a negative value at pos to set the top of the screen 100 pixel to the bottom.I dont really understand this, but works here.