If it's a Gen4 or 5 screen they can uncheck the interior boundary box on the section control screen. 

How new or old is their screen? 

For the future I'd not make the boundary like that since interior boundaries are meant to be spots not farmed. Waterways, terraces, ponds, wet spots, etc. 

Maybe make 2 field boundaries or 2 completely different fields. One where the exterior bdy is the irrigated circle. Another one that's just the corners or all of it.