The "natural" slider causes them to sag. Reduce it. Also, play around with the diameter slider too.

I often spend HOURS fixing breasts of canned characters. There are few add on breast morphs out there, but I find I mostly use the G8F sliders that come stock with Genesis 8.

I've never tried the previously mentioned methods, but I will now. But, most of the time, the sliders do the trick for me.