I have the same unit as yours. I just made my own velcro strips. In that picture I have
ace bandage wrapped around cotton wrapped underneath the glans.
Even if you don't think you may be getting a stretch, you probably are. I'd worry about getting the device on and wearing it for 3-6 hours a day for a few days WITHOUT (your perception of) a stretch. Just make microadjustments accordingly.
I feed velcro through the two slots of the headpiece and attach them to velcro pieces that I had glued to the sides.