Still within the 20 liter volume that is considered SFF; and if you are putting a 280 radiator in there, well, that makes for a larger overall volume...
Yes but that's on the very large side of SFF. The Ghost with a large tophat is just 11litres...
A 240 mm radiator would be perfectly fine IMO. No need to make it excessively large just to accommodate a 280 mm one.