The distance for joysticks will vary depending on how you hold the stick for a particular game.
For the above mentioned games, I don't need ANY for the joystick.
I hold the stick with my middle finger on the left, my index finger over the top, and my thumb on the right.
For button games, like Asteroids, I need at least 6-1/2" from the center of the buttons for it to feel comfortable.
Any less than that, and it gets uncomfortable holding my hands up the entire time.