Rear Vision spell and helmets, again

Score one for my Rear Vision house ruling.

GURPS Magic Items 1, pg 27, has Sense-Enhancing Helmets

"Note that Rear Vision cast on a helmet will be ineffective unless the helmet also has Glass Wall or Invisibility, or the helmet has an eye slit in the back."

That supports the idea that the spell gives a vision ability but doesn't circumvent obstacles to that vision. I know some might argue the phrase "on a helmet" but the alternatives are a weapon or jewelry, because we're talking magic items. That doesn't mean the subject of the spell is the helmet any more than a helmet with Great Voice or Far Hearing on it puts those spells onto the helmet's ability to speak or hear. Magic items generally put an effect on the wearer or another target, not the item.

The working helmet on the same page that uses Rear Vision also has Glass Wall on it.

The book is admittedly for 3e, not 4e, but the spell in question in unchanged from 3e, so there you have it.