Printing to custom size paper from Designer results in larger than expected output

[Travis Miller]

The problem I am having has to do with my printouts printing larger than 100%. Even though I scale my pages to print at 100% in the print dialog box, my printout comes out larger and I think it's a bug relating to the custom size papers I'm using.

I have a Designer project document that is 9.5" x 13" (half of a sheet of 13" x 19" paper) in size. Anytime I print to a sheet of paper cut to that exact size, the resulting output is too large. So, my project gets trimmed down to 4" x 11.4375". When I print with scaling set to 100%, the final trim size width of 4" becomes 4.125". If I print the same project to an 11" x 17" piece of paper, the printout and the trim size is at the size it's meant to be, 4" x 11.4375". 

This issue is driving me crazy! I'm running macOS Sequoia 15.3 (beta) and Affinity Designer 2.5.7. It started happening when I bought the printer a few weeks ago. My Canon iP8720 worked fine with custom size sheets, printing everything at an accurate size. I've tried uninstalling and reinstalling the printer, resetting all custom paper size settings, and updating the firmware to no avail.

Can anyone verify that they having the same problem? I'm using a wide format Epson ET-8550 printer that's capable of printing 13" x 19" media.

[Hangman]

Hi @Travis Miller,

Just trying to think of the obvious things here which I'm sure you've already checked and double-checked but when printing to your 13" x 19" paper stock, is the printer set to borderless printing?

I ask as that could enlarge the printed output size and A3+ (13" x 19") is one of the default Bordlesss Print sizes for your printer...

Regardless, the issue will be with the Print Driver settings rather than Designer since the Affinity apps don't directly control any aspects of the Print Driver...