Distinguishing A5 and STMT Paper
When A5 or STMT paper is loaded in the paper drawer, you can set the size to use for the operation.
1.
Press 
(Settings/Registration).
(Settings/Registration). 2.
Press [Preferences] → [Paper Settings] → [A5/STMT Paper Selection].
3.
Select [A5] or [STMT] for each paper drawer → press [OK].