The XPression Desktop Preview engine outputs 1920x1080 by default. I have forwarded this question to the XPression team for further comment/ideas.
In the meantime, you could add the following code to your Custom Panel to adjust the preview to stretch to fill the entire widget instead of maintaining a 16:9 aspect ratio - this should allow you to make the box 3x wider to see something closer to your desired output.
<ogscript handles="onload">
//Workaround to force DashBoard's preview widget to fill the entire space instead of maintaining 16:9 ratio
ogscript.setStyle('PREVIEW_WIDGET_1', 'bg-fill:both'); // Channel 1
ogscript.setStyle('PREVIEW_WIDGET_2', 'bg-fill:both'); // Channel 2
ogscript.setStyle('PREVIEW_WIDGET_3', 'bg-fill:both'); // Channel 3
ogscript.setStyle('PREVIEW_WIDGET_4', 'bg-fill:both'); // Channel 4
</ogscript>#DashBoard