How to set scaling for source viewer

Hey guys -
I'm working in an anamorphic project with a resolution of 3840 x 1634 and I'm able to get my drone footage shot in UHD (3840 x 2160) to look fine in my timeline. However, when I double click on the file to look at it in the Source Monitor or from the Media menu, it doesn't take up the screen. Which setting affects this?
I have both of my scaling options set to Full Frame with crop.
I'm working in an anamorphic project with a resolution of 3840 x 1634 and I'm able to get my drone footage shot in UHD (3840 x 2160) to look fine in my timeline. However, when I double click on the file to look at it in the Source Monitor or from the Media menu, it doesn't take up the screen. Which setting affects this?
I have both of my scaling options set to Full Frame with crop.