Yes is is modded. The stock clip is curved in the horozontal but not the verticle. This tends to lead to the tacking getting lost more frequently in looking up and down.
I used large gauge aquarium tubing, cut it to length, and used about ½ of the diameter and glued it to the metal clip. I made sure to follow the existing curve in the 'Y' axis, and glued it so the 'X' axis is about a 45º arc (from its initial 80-90º portion....it smushed a tad. I found that a drop of super glue to soften up the rubber tubing to allow good adheasion, followed by contact cement holds very well.
I cover the new area with the smallest 'grain' silver reflecto tape from an autoarts store. The key is that the small grain gives good reflective properties at all angles. The stuff actually looks a lot like the naturalpoint material...but comes is a roll several feet long for less $$$$.
I find it works pretty well. The TIR Vector needs to be as far as practical from your head. because it tracks three points that are a few inches appart, its easy to go outside its 'fiel of view' with one of the 3, and lose tracking. be sure you callibrate with the tracking dots view so you can get a REAL center and minimize issues. I tend to callibrate with more bias to looking up, since theres a plane in the way looking down
