For the iPad touch controls, I recommend adding an extra "fire weapon" button on the bottom left side of the screen. This will allow the player to aim the weapon with their right thumb, and fire the weapon with their left thumb at the same time. It is inconvenient for the player to aim a weapon (such as a sniper rifle) with only their right thumb and fire with the right thumb. This applies only to players who use one-handed weapons, not dual-wielding.
I can also recommend moving the bottom right "drop item" button. When playing the game using touch controls, I often accidentally press the "drop item" button instead of the "fire weapon" button and will drop my weapon in the middle of a fight. Very annoying. Perhaps move the right "fire weapon" button closer to the edge of the screen.