There are 2 ends to every muscle. It's like pulling a string. You cant put one end in tension without the other end being in tension. You can't build half a muscle. Work the whole thing. The shape is the shape.
Not true. Anything that makes the tricep grow will give it whatever shape your genetics determine. Just as with the peak on a bicep, some people have it, some people dont. It is based on genetics, not the type of lift you do.