Use external positioning system for higher accuracy

I was more thinking about how much the code will “trust” my position information. I can easily understand that the EKF gives less importance to a 3d Fix GPS than to a RTK Fix GPS but is this really the case ? If so, are there any accessible parameters ?
I’ve started a more specefic thread concerning RTK and arducopter and some questions I have about this topic (How does Arducopter deal with RTK data)

Anyway, thank you for your help and I hope my question is a little more precise now.

Best regards,