Are HVAC attic to ceiling duct connections a significant source of heat loss?

2012 IECC has just changed the recommended R rating for homes north of the center of the US from R38 to R49. But there is no mention that I can find about the heat loss up through ceiling openings that are connected to standard HVAC R6 duct. Is that because the loss is so small as to be negligible? Have I missed important news about this? 

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BSEE from USC a few decades ago, and now researching highly insulated attic to ceiling interfaces to meet the future need for R49 and R60 thermal performance. Just applied for a patent for a ceiling interface for air ducts that is capable of offering greater than R60 performance. It combines modern advances including a thermally broken duct assembly and trapped air and aerogel for low thermal conductivity, simplicity and easy installation.

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