Tile 1x1 does not make any sense.
That would mean that each pixel on it's own should be fixed by RealESRGAN.
Personally, I would say anything below 256 does not make any sense, but I'll look that I'll limit min to 32x32.
Cu Selur
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Dev versions are in the 'experimental'-folder of my GoogleDrive, which is linked on the download page.