Currently, if the image is a different size it would appear as such. There's no way to force it to scale to a previously scaled size or preset. You'd have to make a feature request for that. Otherwise, you'll have to scale images in advance. Forcing to a scaled size opens up the potential for problems because in some cases you'll want to scale, sometimes crop, sometimes a combination, sometimes letterboxing might be acceptable, sometimes not. It's really best to sort that out in advance otherwise there would be a very complex import scaling mechanism.