Digital BW, The Print

I have been experimenting with QTR and find it very good for neutral 
B/W no metamerism.

I have a problem with uneven margins with a 12x18 image printed 
landscape on EEM 13x19. The top and bottom magins are equal and 1/2 
inch.

The left margin is 3/4 inch, the right is 1/4. 

The image is 12x18 at 300 dpi.

The bat file set paper to SuperB with no additionL MARGINS.

Any ideas on why margins are unequal?

Frank