Titorteat, one thing good about morphs is that we don't have to worry about things like reality and gravity. It's just fantasy and fun and I wouldn't worry about what's "supposed" to be a quality morph. Each person decides if they like a morph or don't like it and different people have different opinions about any morph.
For sure, though my own preference in morphs is for them look as ”real” as possible. Ideally as if the image has not been retouched at all – even if the lady in the picture would have absolutely impossibly large breasts.
I also don't think that shrinking the girl's body makes for a better quality morph than expanding the tits.
Expanding a raster image will decrease its quality. Since the size of the morphed image is not very important, the loss in quality can be at least partly mitigated by making the image smaller after the morphing has been done.
I find it much easier to expand the chest and then make changes on the body depending on what the picture is. The picture of Beshine that we both morphed has a complicated, detailed background and I would find it really hard to morph it by shrinking the body.
Well, if you have the same image on 2 layers, make the background layer smaller and then mask the top layer (and edit it using Liquify or whatever in Photoshop) to only show the boobs, the details behind the girl do not matter that much or at all. The challenge in that case would be to seamlessly meld the body and the chest. In the pic we morphed the most problematic part in my opinion is the piece of clothing Beshine is holding, but its difficulty not related to whether the tits were expanded or the body shrunk.