[BillA]

ask AS about AS stuff

heat transfer is primarily through the actual contact points as I understand the literature,
the flatter the surfaces the greater number of points and/or area of contact
a uniform film of 0.001" w/o any substrate contact would be a pretty good insulator, easily demonstrated by removing the film
"uniform film" is an (imaginary) assumption requiring 2 absolutely flat surfaces

TIM testing is a specialty of its own, lots of info on how to do it;
see Inco's testing for some TIM values, I defer to him

EDIT
you said "need to be accounted for"
I'm not suggesting a calculation methodology which is what you seem to be driving at

rather an awareness that the number of variables not explicitly quantifiable necessitate temperance in the making of assumptions/conclusions