Look at your Keyboard. Even the most ergonomical designs are very much
straight lines (barely any curve). Compare the curve to whats seen on some of these CPs, and its just way too much.
I once had the bright idea to position the buttons in a curve. Thought it would
be more comfortable. However, after mounting them and actually playing some
fighters... I found it was quite the opposite.
I kept instinctively hitting the outside edge of the outer buttons (rather than
hitting them all in the center of the buttons). Which was uncomfortable, and led
to it being poorly hit or a slip.
What I didnt realize, was that when you play a game, your fingers
hover over the buttons at a near vertical 90 degree angle. This gives you
mechanical advantage of shorter distance, use of gravity, etc.
With a curve layout, your center fingers end up being extended outwards at more
of a slanted 45 degree angle, AND, because they are extended further, its hard to
extend them even more without a lot more fatigue. You fight more against gravity,
and lose mechanical advantages, as well as loss of speed. PLUS, because
the fingers have to use two different angles to hit the buttons, (2@90 , 1@45)
it makes it even more straining. Close your eyes, and you can know where
a button is when there is a straight line. But a curve? Not so easy to get right,
if your finger loses contact for even a moment.
Finally, button spacing should be as close as possible. If buttons are spaced even
2 mm too far... there will be stresses on the fingers... which will cause strain
and fatigue. Even if YOU have a monster sized hand... someone with smaller
hands who comes over to play, will not be able to use your CP happily.