CDOCKSEY, you do missing the point. The carbon build up is on the inner side of the valve, the side facing the intake not a combustion chamber.
Dear OP- Knalex01, would you please post some pictures of contaminated valves. It should help the crowd to get a better understanding. If you really want have the understanding of the issue, type "GDI engine issue" in Youtube. Articles are plentiful and very educational.