Archibald said:okay, dumb question time: why put the arms of your sunnies on the outside of your helmet straps? What's the logic behind that?
'cos it's PRO, innit.
And that, as Willy Voet said, the straps can compress the frame against your head, which can be a nuisance in a crash if the straps tighten significantly, snapping the frame and embedding this in your temple.