Digital BW, The Print

I'm getting started with an Epson 1430 with the Eboni inks.

To get my feet wet, I got some cheap Staples photo matte paper simply 
to experiment without wasting a lot of $$$ on paper.

Today I tried some older Epson archival matte paper.  I was surprised
that the exact same image looks sharper on the Epson paper.

I'm trying to rationalize what the root causes of this might be:
  - paper surface texture
  - paper bleeding the ink
  - too much ink being loaded onto the Staples paper?

Maybe someone could shed some light on this for me?

Thanks!

John P