The Epson driver imposes unequal margins. It allows you to print as close as 0.12" on all sides except the trailing edge. The printer needs to hold on to a certain amount of paper to maintain traction while laying down ink near the end of each job. By default the driver reserves a full half inch on the trailing edge of matte papers, but this can be decreased in the driver under the Paper tab by setting Printable Area to Maximum.
From the on-line reference guide
The minimum top margin is 3.0 mm (0.12").
The minimum left margin is 3.0 mm (0.12").
The minimum right margin is 3.0 mm (0.12").
The minimum setting of the bottom margin is 14.0 mm (0.55").
When printing near the minimum bottom margin, some colors may not be printed properly. If this occurs, try increasing the bottom margin.
* You can extend the minimum bottom margin to 3 mm by selecting Maximum as the Printable Area setting on the printer software's Paper menu (Windows) or in the Page Setup dialog box (Macintosh). However, print quality may decline in the expanded area. Before printing large jobs using this setting, print a single sheet to confirm printout quality.
* When printing with the Borderlessfeature, print quality may decline in the top and bottom areas of the printout, or the area may be smeared.