I have mounted many fenix lights to my helmet.. The lockblock is not the ideal mount for this.. The bikeblock which has parallel mounting and a larger velcro strap works great.
I found that the zefal doodad plus is the easiest mounting.. The doodad gives more flexibility to aim the light a little higher. Both are super secure, the doodad plus is a little more minimalist.. I found a good source for the doodad +, from genuine innovations, the co2 people..
It is best when ordering a fenix that you should order 1 bikeblock and 1 lockblock.. Depending on your helmet, one will work better than the other..
http://www.genuineinnovations.com/bi...=5&prodid=1044