It isn't discussed because a throttle body is simply a straight pipe with a butterfly valve mounted in it.
Increases in air flow are directly proportional to the increase in the inner diameter of the throttle body.
Unlike heads and intakes which typically have various diameters and radii which make simple calculation of airflow impractical and therefore necessitate live measurement of flow.
Plus under WOT, the surface area of the throttle opening doesn't change, unlike heads, which have valves that continuously open and close.
"[I do not] carry such information in my mind since it is readily available in books." - Albert Einstein
2013 Mustang GT, M6, Tech package - Bone Stock