I've got an Arai Signet-Q as well, that I had the Drift HD attached to. I put the mount directly on the top between the two vents, just back from where the visor, in the up position, would fall. Worked out perfectly, and laid nice and flat (compared to my GoPro). So, that's another option, if you don't mind the cam up top. What's nice about the Drift, is the lens rotates, so you can mount it horizontally or vertically. Up top gave me the best POV, and was easiest (but doesn't work well on the RS-1).
When you mount on the side, it takes more tweaking, and you do have to settle for that off-center perspective, with the upside being that it looks "cooler" and more aerodynamic. Although, with the cam hanging off one side, and my Sena SM5 off the other, it looks like I'm wearing a helmet with the mumps... (but the vids are worth it, in the long run).
Thank you for the pic! I have the Arai Rx-Q helmet. I have been playing with the curved mount trying to figure it out. The only part where the whole thing sits on the helmet "flat" is just behind and below the visor side plate or Right on the visor side plate. I dont think the visor side plate would be a good spot for the rare chance of the plate coming off. But just behind and below, it looks like it will be angled SLIGHTLY outward, and not pointing exactly straight ahead. But the FOV on this camera will make up for that by still giving a good straight ahead shot, right? Wish I could take a pic of this! I was leaning towards putting the opening on the mount forwad (thinking that any wind wouldnt give extra pul against the snap in). I am also thinking of lanyarding it to my chinstrap.