Forum of the article
I see that, following your article, Jason Colavito also wrote on a similar subject, and that there were quite a few comments on his article (including several from you).
But still no one seemed able to thrown any light on the question of where exactly Agatharchides wrote about the dimensions of the Great Pyramid ... :(
Ah, but I have no doubt that, sooner or later, Jacques Grimault will provide us with his source. After all, he claimed more than once that his source was Agatharchides himself, so that I suppose he has found an unknown papyrus of Agatharchides or Artemidorus :)
The above link being broken, here is a screenshot of Jacques Grimault’s claim that his source is Agatharchides...