Stop messing with aluminiun bumpers. All of them will mess you signal and wifi. I had used and tested over 12 alumini bumpers including the Thanotech K11.
All of them affected my signal. The K11 had the smallest effect on signal but it did affect.
Best option out there is Rhinoshield CrashGuard...
Great point on the aluminum. I wouldn't have thought it, especially due to the rubber/silicone between the aluminum and phone itself in most common models.