Click depth or internal links: which says a page is too deep?

Click depth is the number that gets reported, and on its own it is the one I trust least.

A page four clicks from the home page with sixty internal links pointing at it behaves nothing like a page four clicks out with two, and a crawl reports both as depth four. On the large ecommerce sites I have worked on, the deep pages that rank are almost always the ones that collected links from related products, guides, and category copy. They are rarely the ones that sat higher in the menu.

So the number I look at is inbound internal links, split by where they come from. Links from a navigation template are cheap, because every sibling page has exactly the same set. Links from body copy are the ones that separate two pages sitting at the same depth.

What I have not settled is a threshold. I can say with confidence that a page carrying two template links and nothing else is under served. I cannot say whether the target is five body links or fifteen, and I suspect the honest answer is that it scales with the size of the set the page belongs to.

If you apply a rule here, I would like to know where the rule came from. A number someone measured is worth more than a number someone published.