There are a couple of pieces of information that I'd like to have in order to understand what's going on.
Are you on MacOS or Windows? Are you printing using the Epson Driver or QuadToneRip? If using the Epson driver, do you have a finest detail setting and is it checked? What colour space are your images in?
Depending on the answers to these questions, it's possible that if you send a 360dpi file to print then it is being upsized by either the OS (Mac) or the driver (Windows) to 720dpi.