I've tried just about every possible place to mount a camera on a mask. Left, right, top, visor, right side of visor, left side of visor, under visor (sticks out really far) and even on my nose...
The best I have found is with the lens between your nose and your left eye. (has to be between your eyes, as you lean out enough for both of your eyeballs to see your target, so you can judge distance). If you center it exactly, you end up getting hopper shots, but if you move it over another inch, it will still pick up everything, and get almost no hopper. A low profile hopper obviously is better (tippmann A-5 low profile hopper works great paired with a cyclone).
You need something on the back of the camera to keep it from bouncing when you run. I used to use duct tape, but now I use a zip tie, as it is reusable, and works better.
Here is what you can expect with it mounted like that. (I film in 720hd with the 170 wide angle setting, you can go to 1080 and get a smaller field of view, but I personally like the widest angle as it shows more of what is going on.