I want to resize the embedded VCS in the main layout. I think my issue is that once a VCS layout shrinks, for whatever reason, you can't grow it again.
You can use the VCS editor to increase the size of a VCS widget by using the editor's width and height fields found in the bottom right corner.
In this case, unlock the VCS to open the editor, select the embedded VCS layout, and set the height of the widget (the bottom right text field in the editor) to the height you need.