>>936005882
Pretrained upscale models only upscale at set sizes, generally 2x or 4x, so if you want something less than either of those but still more than the base res you need to downscale the image out of the model.

For example, if you only wanted 1.5x the base resolution you can use a 2x model and then downscale the resulting image by 0.75x.

2x * 0.75x = 1.5x

This also saves time at the higher resolution as the gen time increases with resolution.