What you are calling the vertex, commonly referred to as the crown, can be a black hole for follicles. By that, I mean that it can take very many follicles to fill it in completely. So, it all depends on your available donar hair, the area you want covered and the desired density. If you are comfortable with some thickening of your hairline and front, along with some thin filling in of your crown, then you might be ok. But for a Norwood 6, it becomes increasingly difficult to give good density to all of it. I don't mean to discourage you, but that is the reality. Having said that, the top doctors can really make a cosmetic difference in your hair with a quality transplant and aesthetic talent.