I have some that are teardrop-shaped. I found the same thing that they add to the projection, but not the circumference. Typically, (assuming a flat chest), they would be worn with the narrow side up, or slightly angled toward the armpit. What I found is that if I turn them 90 degrees so they lie sideways in the bra, it gives the added width and pushes just enough to add cleavage. I wore them that way all the time, and it felt more comfortable and looked more natural.
Then HRT kicked in, and they just don't fit anymore. The backs are flat, so there is no room for my natural curve beneath them. I switched over to "swimmer's" breastforms, which are triangular-shaped with a curved back. They were much more comfortable, but, like the others, they were too hot and sweaty in the summer. I haven't worn them in over a year or more.