There's always a large black border all they way around it. This isn't the scaling problem I've had with other games where the monitor is shrinking the display area down. I can see the display area around the game screen in a slightly darker shade of black than the borders on the far left and right due to the game being 4:3. So for some reason, the software itself is only displaying in a small area in the middle of the available screen.

Find file called dosboxishar1.conf in folder where is your Ishar 1 installed and open it.

At the beginning find this:

fullresolution=original
windowresolution=original
output=overlay

and change to

fullresolution=desktop
windowresolution=original
output=overlay

I also changed output=overlay to output=opengl

Hope it helps