I had no problems getting the previous adventurersworkshop small ADV sticker on my Arai... these were also the thick 3M reflective stuff...
A) cleaned the helmet really well, using some windex and lots of elbow grease.
B) put both the sticker and the helmet in the sun on a hot day for a good hour, til they were almost too hot to touch
C) only partially removed the sticker backing, started at the top edge, and 'stretched' the sticker as it went around the helmet... I used my thumb as a pressure roller, and pulled any wrinkles out BEFORE the stuff touched the helmet, while incrementally pulling the backing out from under the sticker.
this also worked for the large ADV applied to the windshield of my R1100RS, only that took two tries, the first sticker got away from me and stuck with a horrible big crease, so I used my heatgun judiciously to peel it off, then lots of goo-be-gone and wd40 to remove the residual adhesive, and started over with a new sticker at step A (really thorough cleaning to remove the oily stuff)