Canon ir5000

Question

good day.. i want to ask a solution for our problem.. our machine is canon ir5000.. the problem we encounter is.. if i use the ADF, with long size 8 1/2 x 13 paper, the detection of output copy is LGL or 8 1/2 x 14 which results to 1 inch blank copy on top of paper and the bottom is cut. ( i thick the we have to do some program adjustment to detect the 8 1/2 x 13 or FLS when using ADF) .. there's no problem when we use LTR and A4 and no problem also on FLS if we use platten glass. thank u very much for your help.