Trouble with incomplete images using Watercolor RW and rear feed

I have a r2400 and I am trying to print on 13x19 watercolor radiant white. I downloaded the right drivers and everything is printing well except for this paper. It requires the rear feed and when I print image starts about 1/4 down the page. I am left with a large border on one side and an incomplete image on the other. The printer manual says to select roll paper as the paper type but I don't even have the option to select the paper type. There is no drop down menu. And in any case, it isn't even roll paper. What do I do?