I printed the 2"x4" test image on my Epson R1900 at PhotoRPM (the highest resolution on that printer). I used Premium Photo Glossy paper to preserve crisp edges.

The printout was scanned on my flatbed scanner at 2400 dpi. Each section or block of the image is roughly 0.3 inches across.

These are two pieces of that scanned printout that encompass a section of 'faux 360' portion and a similar section from the 720 side.

I think its clear that this Epson printer is capable of significantly higher resolution than 360ppi. In my mind this adds more credence that the native resolution of this printer is actually 720 ppi.