Imgsizer limits?

I’m trying to use imgsizer to create backgrounds for my post pages, and in order to accommodate large displays I’m trying to get a pretty large image output, 1920px width in this case. What I get however is a blank page. The largest width that works is 1797px wide.

My PHP memory is 256mb (local server, I’ll have to tweak the production server I’m sure)

works:

{exp:imgsizer:size src="{image}" width="1797"}body, html {background-image: url({sized}) !important;}{/exp:imgsizer:size}

does not work:

{exp:imgsizer:size src="{image}" width="1798"}body, html {background-image: url({sized}) !important;}{/exp:imgsizer:size}

Thoughts?

[Mod Edit: Moved to the Plugins: Discussion and Questions forum]