When I originall drew it I had them all facing the screen. Then I printed out the CP full size and stood around it trying to get a feel and it just felt awkward with them not rotated. But without actually playing a game like this I can't be sure. If I rotate them back so it faces the screen, should I move the buttons around as well? With the sticks facing forward the button placement felt too high. It's hard to explain.
I know what you mean. I thought it seemed an odd layout as well. I eventually mounted all 4 joysticks' UP facing the top of the CP (as the people on the board suggested) and playtested it with 3 other friends. They didn't have a problem with it, even though my 3/4P are at rather sharp angles.
My artwork highlights the positioning of the buttons to joysticks (they're all uniform). It's not often that P3/4 are used, but when they are, I've had noone complain. I'd personally not change your distances from the joysticks/buttons, but do whatever feels right for your cab.
Another idea would be to get 2 people both playing a game (P1 & P3) and see what they think. You're likely to be much more critical of the placement than others are. If the "All joysticks UP" layout seems natural to someone "off the street", then you're good to go.
Also, if you're thinking the buttons look "off" because of your diagram, try removing the rectangles from around the joysticks... You won't be seeing them on your final CP, will you? Also, P3 would be standing at an angle from the CP, so his left arm would be perpendicular to his button-rows, so his arm shouldn't ever be interfering with his button-smashing hand.