I use the Mail Merge feature in Word to create checks to print.  The amounts are all the same in each run; e.g. 25 recipients, each in the amount of $100.00, so I don't have to worry about numbers-to-text.  
I use pre-printed fan-fold checks on a dot matrix printer.  I set the paper size to "Check" and confirm  that the check is 8.5 X 7.0 inches.  I also measured to confirm the checks are indeed 7 inches.
My problem is that the printing on the checks gradually creeps up the page, check by check.  I can't print more than 5 or so in a batch without moving up a whole line.    Our runs are 25 - 300 (sometimes more), so I would like to start the full run and just watch for jams.
What am I missing here?