Kunze states that the malt and water will naturally set up a pH of 5.6-5.8 which should be lowered to 5.2, but also that extract potential is highest at 5.4-5.6. He doesn't have to mention temperature. Nobody does. It is, and always has been the pH at ROOM temp that is the reference. The article that started this is bizarre, but not surprising given what it is, and the passage from Briggs et al is hard to explain or to understand really. But Briggs again is not a reference to be sought out for modern, even British, processes and materials. (But I don't think it can have meant what it seems to.) You can look at any text -- DeClerck, Kunze, Narziss, whatever -- and the matter is settled. The texts are not at all vague or confusing, none of them. The BYO Wizard guy is vague and confused.
Siebel sells DeClerck reprints pretty cheap, and can get you a Kunze for under $300 including shipping.