thanks!
No, you'll get the full 100. You can even reflect more than 100 percent. The armor effect is only on spells you cast.
It's tied up with the way that reflected spells can't be re-reflected. If they didn't remove some of the complexity at each stage of the cast/receive process, it would get silly.
However, casting a Reflect spell would get its effect diminished in that way.
Spell efficiency only affects spells that you cast, not spells from enchanted items.