I would like to test this on my P800. I have printed many sizes with no issue, 4x5, 5x7, 8x10 and 16x20 on 17x22 paper with no issues. But I haven't tried 13x19. My usual machine is a PC, but I will try it on my 2015 MBP with High Sierra.
I take it from your post that you are using 13x19 paper. What margin settings are you using?
I made two test prints:
13x19 Epson ultra premium lustre paper
1/2 inch margins.
2015 MB High Sierra, LR CC CL V 8.0, First two prints with Epson driver 10.01. Third print with current Epson print driver 10.16. The driver version made no difference.
See the photo. All three prints printed with the designated 1/2" margins on the sides, but the top margin was 0" and the bottom margin 1". All settings were triple checked. As you can see on the MBP screen, the preview has equal 1/2" margins all the way around.
Since I almost never print from this MAC, I'm not going to put any effort into fixing the problem except for updating the printer driver which made no difference.
I thank you for taking the time to reply to my post, and I'm sorry for taking so much time to reply. I was under a tight deadline and very frustrated last week. I finally reached an Epson support person and after an hour of on-phone support discovered how to rectify my issue.
The solution was not because of my page setup sizes or my margins or anything else related to Lightroom. It turns out that there is a "bug" with Epson's OSX P800 printer driver when you use saved presets. I had a ton of Print Presets for the P800, like I've had for other Epson printers. These were for fast contact sheets at 1440 dpi on luster paper, highest quality prints on exhibition fiber at 2880, cold-toned black and white prints using ABW on glossy paper, etc. It turns out that while it appears that the presets store your print quality and media settings, they wreak havoc with page layout and in many cases contributed to the margin printing issues I was having. The technician told me that the best practice was to use Default Settings and change all the settings manually for each print type I did, a pain, but something that has worked for me every time since then, no matter what paper size, media, sheet or rollpaper feed, and margins I switch to. The Epson technician would not say who was at fault, Epson or Apple, but did acknowledge that use of the presets was not advised. The Default Settings do seem to remember the last settings you used so you don't necessarily have to start over again.
This solution defies logic, but the fix seems to work for me. Perhaps there is some quirk with OSX 10.13.4 print system and the latest P800 driver, I don't know.
So to summarize, when you print with OSX and the P800:
1) In LR Print Module, check your Page Setup and that you're using the correct page size, whether it be standard ones or custom ones
2) Check the margins in LR
3) Use correct profile for LR color management
4) Make sure you use Default Settings in OSX Print dialog and manually change the Printer Settings for quality, media, etc. and verify Paper Handling is correct or your paper type (Roll paper, sheet feeder, front loading, etc.)
Hopefully if someone else has a similar problem, this will help them.