From the FAQ
http://forum.free-track.net/index.php?showtopic=413
The LEDs fade away when I turn my head only a small amount.
The viewing angle of your LEDs is too small, increase the viewing angle by filing the LED lens tips down flat, almost to the metal part and then make the final finish transparent matte (not too shiny, not too rough). Alternatively you can buy wide angle IR LEDs like SFH485P or equivalent (+/-40 degrees half angle). These LEDs are unlikely to be available from consumer electronics shops, instead try major distributors like Farnell and RS Components or through a specialist like LumiTronix.
Take some sandpaper, spend 30 seconds and flat 'em out
Cheers
Nils