The most effective way to position your breasts to create a shape like a flat chest or masculine pecs is to push your breasts in the direction of your armpits, and slightly downward. You can do this most easily if you first put on the binder, and then lie down on your back, and use your hands to temporarily lift the binder away from your body. That should allow your breasts to naturally fall in the direction of your armpits. If you shop for binders other than those on this list, look at the catalog's picture. If a binder has really large arm holes that are open way down the side of the wearer's body, you can tell that binder is no good. With that design, when you try to press your breasts toward your armpits, your breasts will just bulge out of that binder's wide-open armholes. That's no good for making a masculine or feminine chest shape. This design flaw is common in binders from Japanese and Korean companies. Instead, look for binders that have compression in the under-arm area, or at least have smaller arm-holes. If you have big arms and find that the arm-holes are too small for you, the ideal thing is to customize your binder by sewing.