Running several where I work, I've only found one way to fix the default paper size.
Delete the all of the Epson driver software. Pull the Epson's preferences out to the desktop. Reboot, then reinstall the software. I recommend pulling the latest driver off the Epson website since there are so many bugs in the software.
When you first install the Epson driver software it will ask you what you want your default paper size to be. Select letter. This is the only place to select the default paper size, AFAIK.
From there you can swap in your old preference files one by one if you have already saved specific color or layout settings.
When they work, they're beautiful. When they don't they can be the most annoying things in the world.
---Joe