the best way is to give the players an option to resize the control pad so they can choose the equal size for each device.
Also it's nice to hear that you are adding new features.
Some new enemies like hexagons from asteroids deluxe would be good. But if you are about to add hexagons, you have to tweak the contols too, because the control of this game is quite slow like asteroids than fast and stable like asteroids deluxe or space duel.