Hi jcshjm,
Thanks for the response! Glad to hear an alternate driver helped. Unfortunately for the a910 model, the customizable options are not available for Windows operating systems. If you have a Mac this software will still customize the size. I have clarified below for future users that may be working with the 909 models.
Note to future forum users with similar issue: the previous custom settings are compatible with 909a-g 8500 Officejet series software.
Thank you for being an HP customer!