5DII grid focusing screen not aligned with AF points? & why no horizontal third lines?

I have just fitted the EG-D grid focusing screen to my 5DII. I'm pleased with it, but slightly bothered that the AF points don't seem to be perfectly lined up with the grid. As an engineer by trade I am perhaps oversensitive to lines and squares that don't match up but has anyone else noticed this? I removed and replaced the screen and it seemed to be slightly better the second time, although the screen holder appears to be designed to ensure that the screen sits in exactly the right position. I'm reluctant to keep taking out and replacing the screen as I don't want to get dust in the camera housing as I'm going to a major shoot this weekend (albeit not for money).





I also notice that although the vertical lines show thirds, the horizontal ones don't - there is a line through the middle, and lines through what I'm guessing are the top and bottom 6ths of the screen. Why is this? I'd have thought horizontal thirds would be much more useful, although finding thirds from 6ths shouldn't be difficult.