Tried some new things in DAZ. Currently I'm experimenting with Smoothing Modifiers. I'm not quite satisfied with the outcome. Are there any other ways to achieve better results than this?
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Try using specific morphs, maybe even together with smoothing modifier. Maybe some of the dforce breast products, but the ones with addons often give not so great results, in my little experience with them.
From some interaction I had in the past with the DAZ Support, from one side everybody uses the smoothing modifier to model impact of objects with the body, even because there is explicitly the possibilty of choosing collisions, but from the other, they seemed to suggest it is not supposed to be used in that way (and so, not a supported use).
The problem (well, not if one get his/her hand on some to erotically play with

;-)) is that breast, is one of the parts of the body who has both fat and muscles, and both of them compress only to a certain point - which, e.g. in in your case, they would be compressed against the glass, but also appear with a bigger diameter than they normally have (volume only partially reduced by compression, and partially redistributed). Also, unless she is completely squashed against the window (that does not seem to be the case), part of the breast would be effectively flattened against the glass, but part of it would not, while in your image, the whole if like a flat surface.
For hanging down breasts, I found various solutions that seem to work well (scripts, dforce addon), for some action position/sequence with no impact, the dforce addon or some scripts went relatively well (but require a timeline simulation of the movement), for this type of situation, or even more, the laying on her back situation, nope, the best I have reached was using a combination of pre-made morphs.