User guide says you can do this, but look out for the 'gotcha's'
To resize a dashboard monitor:
A: Drag the resize icon in the bottom-right corner of the monitor toward an appropriate location.
As you move the cursor, the background outline of the monitor changes shape to reflect the
supported size closest to the current cursor location. Monitors might enforce a minimum or
B: When the background outline has changed shape to a size you want, drop the monitor.
If you attempt to resize the monitor to a shape not supported in the monitor's current location,
it returns to its prior size.
If it's not working as expected you are probably hitting oneof those limits.