What could be a more established unquestioned, unchallenged tenet of Shroud (pseudo)science than the notion that variations in image intensity are related to cloth-body distance? Try googling (shroud “cloth-body distance”) and see the 4 pages pages of returns, 10 entries per page, all deploying, or as I would say, bandying around, those words “cloth-body distance”.
Remove the search-narrowing quotation marks and there are 30 pages of returns in Google (its maximum?) with enshrined references to cloth/distance/body, not necessarily in that order.
Update Thursday: here's the main posting to which the above was a ground-preparing preface.