Hey, thanks for the re-report. This is a known limitation, image generation doesn’t support custom sizes or aspect ratios right now. The 1376x768 size is the provider default, and in the current implementation the tool just doesn’t pass any size parameters.
The team has been aware of this since the original report Image Generation Only Has Fixed Resolution. There’s no ETA for adding custom size support yet, but your re-report helps with prioritization.
As a workaround, you can use external tools to resize the generated images.