One difference between the tiercel and the falcon that I have noticed is that their tail patterns are different. The size difference is very obvious in Alan's photos. She is considerably bulkier than he is.
The pair nested in the centre compartment of the tray last year but this year they have opted for the far end. This is because the tray has been moved a few feet further north up the walkway thus enabling the birds to have a view through a hole in the wall out over Grantham! Quite often the female leaves the tray via this hole.