I'd never had any deductions until about a year ago myself. This month it was 3.7%. Their "estimates" used to be spot on, but now it looks like they need to work on them.
At the very least, some explanation of where the money is going would be helpful. I had hoped that the "new payment system" would tell me this info. Instead, it just seems to give Google a way to take more back once they have finalized the earnings.