Digital BW, The Print

Hello:

I was wondering if anyone had experience using Epson Velvet Fine Art
Paper on an Epson 1280 with Piezography K6 installed? I find that when
I use the 8.5x11 I have no problem and the print is beautiful - better
than HW Matte, with greater shadow detail. I use QTR with the
EpsonHWmatte setting. When I print to 13x19, the ink starts clogging
(I think) before the image is done, and I start losing blacks and
shadows - IOW, I've wasted an expensive piece of paper. 

I alway turn the printer off, and I store with OEM cleaning cartridges
I got off Ebay. 

Any suggestions?