Trying to verify the correct way to bill for a nurse practioner.

Can anyone elaborate on these thoughts:

Unsupervised, I bill under the nurse practioner's number

Supervised visits, I bill under the Doctor's number but use modifier SA, would I select the rendering or the surpervising as the biling provider? And by using the SA modifier does this tell my payors to reduce the payment since this is a supervised vist, OR would I still just bill under the APRN's number?

Any help is appreciated.