Another former amazon manager here, I can confirm this. The rule of thumb was %6 URA target and a somewhat larger number into Focus.

I never saw any written documentation about the URA goal, HR probably wants to avoid creating a leakable paper trail. It always came down verbally from my L8. I heard rumors that Amazon's HR boss Galetti is the big advocate of the URA goal, but I was nowhere high enough to be part of those conversations.