Yes, Peter was the designer of the core. He is a man of perfection and very good at what he does. His development thread is here: small scale development
One of his photos shows exactly how this P channel fits to the core.
As far as cf board, not everyone has access to it or is out of their price range whereas casting can be more appealing to some. Hard to make a trip wire or backsweep from cf board than it is to cast but also much more of a learning curve with casting too. Nice there are options, each with their own inherent benefits and drawbacks.