They used more than the ceiling of the Grand Gallery to reaffirm the calculated height of the structure using a 28:22 seked (4/pi) ratio.
The designers had to guarantee that we would calculate this value for one major reason...they never coated the sides of this structure with angular casing...only the base.
The missing casing is approximately 4Rc on both sides from the second layer all the way to the apex (Petrie quotes an estimated 71 inches).
Petrie confirms these measures at course: #19 entrance, #101 airshaft exit and #201. Note the number 201...does it ring a bell ?
Investigate the height at course # 201 and you have the true height of G2...I don't understand why, but I believe Petrie new that fact but neglected to state it.
By calculation, using the base of G1 and an angle of 4/pi, then the truncated height of "G2" should be 5409 inches. Ironically Petrie selects that exact height for measure on G1.
The courses of G1 "had" to have its casing in step format, it allowed the designers to demonstrate their phenomenal geometrical talent.
I posted previously, several months ago, that course #35 (second thickest) is at the identical height above the base line as the subterranean passage is below the base line, that is not a coincidence...it's by design...!
You have to begin thinking of this complex as a single entity...if not...then you will never see the whole picture.
Best.
Clive