There’s an essay on “Staffordshire and Cheshire Landscapes in Sir Gawain and the Green Knight”, in the book collection of essays The Gawain Country: Essays on the Topography of Middle English Poetry, Leeds Texts and Monographs series, 1984.
The essay is not online, but the book may possibly still available by mail-order for £9 — according to this order page which dates from about circa 2011.
Incidentally, the pentangle on the shield (above) is not a pagan artist’s modern imposition on an ancient text, it’s something detailed in the text…
It is a symbol that Solomon designed long ago
As an emblem of fidelity, and justly so;
Therefore it suits this knight and his shining arms,
For always faithful in five ways, and five times in each case,
Gawain was reputed as virtuous,