Despite wearing a perfectly-fitted bra (I routinely get my bra fitted yearly), I still have back fat. In fact, I notice it more! It's not one of my fussiest bits (still pretty fussy though), but I've worked out solutions for it.
My advice?
1) Well-tailored garments (blazers, shirts, dresses tailored to your measurements)
2) Flowy, looser tops (a-line or blouson)
3) Layering (i.e. Cardigan over shirt, v-neck sweater over button-down shirt)
4) Don't wear tight knit tops (or stretchy wovens)
I've never tried Sassybax before but I heard wonderful things about them. I never tried because I'm a DD/E, and I really can't go without a bra. I think certain shapewear can alleviate the problem as well, but I've always had better luck with the advice I mentioned above.