[TowerTalk] K9YC Choke Cookbook Question

[KD0Q-Glenn]

I have a question about bifilar chokes from K9YC's Choke Cookbook...

Several places in K9YC's material indicates that bifilar chokes wound 
with close spaced enameled wire would have an impedance of approximately 
50 ohms and those wound with close spaced THHN would be 80-90 ohms.

In Chapter 7 of K9YC's  "A Ham's Guide to RFI, Ferrites, Baluns, and 
Audio Interfacing" the table for bifilar chokes shows the THHN wound 
chokes at 50 ohms and 2/3 of those wound with enameled wire at 85 ohms.

I think I missed something as the guidance in the cookbook doesn't seem 
to follow the discussion earlier in the guide and in Jim's slides at 
k9yc.com/CoaxChokesPPT.pdf.  What am I missing? Is there another factor?

Thanks & 73, Glenn - KD0Q