Medicare uses different rules to pay for multiple surgical procedures and multiple endoscopic procedures.  For non-endoscopic procedures, the service with the highest RVU is paid at 100% of the fee schedule, and at 50% for the second to the fifth procedure.  

Multiple unrelated endoscopic procedures are paid using the same formula as multiple surgical procedures. 

Multiple related endoscopic procedures are paid in this way:

100% of the fee schedule for the service with the highest RVU

Second and subsequent procedures are paid the difference between the RVU for that procedure and the RVU for the base procedure in that family of codes.

This is how the Medicare Claims Processing Manual describes the process in its instructions to carriers:

13. If Field 21 contains an indicator of “3,” and multiple endoscopies are billed, the
special rules for multiple endoscopic procedures apply.  Pay the full value of the
highest valued endoscopy, plus the difference between the next highest and the
base endoscopy.  Access Field 31A of the MFSDB to determine the base
endoscopy.