Picture (not file) sizes

Hi, I’d like to use Gigapixel AI on selected areas of pictures I create in Affinity Photo (I’m an artist rather than a photographer, so normal things like faces don’t apply).

So I copy and export an area I want to process as a TIFF.

When I reimport it into Affinity Photo after processing it at 1X in Gigapixel AI, it’s larger and has to be scaled down manually.

Any ideas how to avoid this? The Photoshop plug-in doesn’t work in Affinity programs.

I should add that I routinely increase the DPI 300 and resample images in Affinity Photo early on in the process… but I don’t think that should make a difference.