Re the upper screen grab, don't select 13*19 Poster Board. Just select 13*19 (the top option in the list for 13*19 size). Make sure the driver version you are using is NOT the Airprint version (you'll see this in System Preferences>Printers-Epson P800>(then perhaps into Options and Supplies>General. If the Driver version says airprint, delete the printer in the same window, then re-add it, paying attention to the option that comes up to select the driver version. Choose the series driver, not the airprint driver. Now if all that is OK, when in LR, click on Printer in the Print Module; it should pull up the driver, and in the Print Settings page, you will have the choice of the Front Fine Art Feed for your paper size.