Print size not correct z3200

[Richard_Jones]

On the z3200, when printing from Photoshop or Lightroom using a custom paper size on a 44" canvas roll (1117mm x 30m)

no matter what print size I specify, the print job ends up bigger.  Having run tests and tried every support trick I've found on the internet I keep getting an extra 0.25 of an inch for every 5 inches of print.  Its quite consistent.
When I want to print an exact size (for a white edges canvas frame for example). I get bigger than expected jobs (by 0.25+ inches per 5 inches).

I've tried, different apps, custom papers, (the roll is 1119mm by printer calculation) and I've tried 1116/17/18.etc.., I've not changed the applications print DPI at all, why should I? all my other printers put out exactly what the print job size is or is this the important part i'm missing - normally I set the applications to print at 600dpi.. should I be looking at native print resolutions?.

I could just work out the add on per inch and subtract from the print job but I'd prefer to type in a number and get that printed!

I've searched a lot and found lots of advice which I've been through. I'd appreciate any help (however basic) because I'm clearly missing something obvious.

Hope you can help...

Richard