If you have buried and encapsulated the duct distribution system in the attic, please use the measured insulation value on the improved side of the ductwork recommendation to enter the final insulation R Value of the ductwork.

Please refer to the following articles as reference on how to calculate the encapsulated insulation R Value of the ductwork:

Building America Solution Center

Ducts Buried in Attic Insulation and Encapsulated

DOE Building Technologies

Measure Guideline: Buried and/or Encapsulated Ducts

Burying and/or encapsulating ductwork in attics can reduce ductwork thermal losses to around 3% or less. Under this family of duct insulation approaches, ductwork may be encapsulated in closed-cell spray polyurethane foam (ccSPF) insulation and/or buried beneath loose-fill insulation. Buried and/or encapsulated ducts (BEDs) reduce duct thermal losses without affecting living space or increasing thermal envelope loads.