It's a basic geometry math question;

IF "X" = the land surface of all the earth then where does the intersection of 4 equivalent quarter-spheres (each containing X/4 Sq Kms) lie?

You can't do it with 2 hemispheres because the solution would be anyhwere along the base line.
You can't include the oceans because the answer becomes anywhere you chose to place the 4 quarter-spheres intersection.

Be a pain to actually do the math though.

For the theory to hold the AE somehow chose the Giza plateau because it lay at the center one would first need prove understanding, ability to calculate, and intent.

Jammer