The print driver allows many sizes to print from the tray. More info is needed to accurately answer your question.
What size is a full sheet?
How many checks per sheet?
If one check is printed from a sheet, what size "sheet" remains?
If two checks are printed from a sheet, what size "sheet" remains?
The print driver also allows you to create custom paper sizes. If the tray can't handle it, the manual feed can. By the way, this is an EXCELLENT printer. Very pleased with it.