I don't get the button configuration?
Ah....the button configuration.
My mockup CP had 6 buttons per player (fighter style), and after a test run, I decided that I didn't like it at all.
Of all the old games, there was two that I could think of with "different" button configs, those being Defender and Asteroids.
The "long thumb" button as you put it, is really a reverse button for Defender, to be hit with the left thumb. It will also come in handy for Battlezone as well.
It was a bit of a pain to install the reverse button as I placed it fairly close to the joystick (I had to scalp a bit off of the t-nut).
I only really needed one of the reverse buttons, but I wanted the buttons to be identical on both sides.
With the 5 buttons, I can still play Asteroids effectively.
To get the spacing of the four "right hand" buttons, I just placed my hand on the CP, and marked them.
It may not look it, but a lot of thought (and indecision) went into this