There isn't a way to make the pan-pot larger, but you could change it to a different widget type. For example, find MultichannelPan XY coordinates with Doppler in the Prototypes (search using Ctrl+B).
In the VCS, Ctrl+Click on Position and select widget type: 2D Pan Pot.
That will give you a larger circular XY control.
You could try using !Angle and !Radius as your controls. In the unlocked VCS editor, select !Angle and !Radius and make them an aggregate (Select Make Aggregate from the Widget Type list).
Then select Widget type: 2D Pan Pot