I'm absolutely convinced they made P and P1 matchday tickets only because once the expansion is done they are going to shift the away fans round slightly more into the North stand. They need to get the away fans out of the East stand to stop them standing in front of the new boxes, so shift them round a block or two. There's no current ST holders in those blocks like you say, so no moaning about "this is my seat" when those seats become the away end.