Hi Andy,
Can't talk specifics, but if you were able to print full length of sheet, then you would get ink on the platen - paper size/feed is not too precise. Ink on the platen equals messy next prints, so Epson set the sizes as large as they dare. If you were to tape a sheet on the back of your paper, longer than the length of your paper, then set a custom size, you could probably get what you want, and possibly gat a bonus of a few paper jams too
Some folk do similar to feed canvas through lesser printers.
Best wishes,
Ray