It just depends on what state your policy is underwritten in & what provisions your employer selected. Usually most insurance companies now have "specialists" for certain covered benefits so that way you know you are getting the most accurate information since that person deals with that benefit all the time.
Also check with the financial person (billing, claim or insurance specialist) in the doctor's office to find out what is the average expected out of pocket cost for your plan.
When I worked in the medical billing & insurance field, not one single patient had the same policy benefits & that made work hard since we would have to call for benefits with every single patient, every single year.
You can figure that if your co-insurance is 20% that depending on the total cost you probably will have to pay $1,500 to $2,500 out of pocket.