Jon:

A "cube" containing 33 units (outside count of stones) has a width of 3.2 stones (cube root of 33).
A "sphere" having a "diameter" (equal in width to the cube) of 3.2 stones will have a volume of 17.3 units (inside count of stones).

Rhind Mathematical Papyrus #50 states that a circle of 9 units width will have an area equal to (9-1) squared or 8 squared = 64 units. The 9/8 ratio is an approximation and when squared it equals 1.2656...the true ratio is actually 4/pi...1.273:1...a very familiar ratio at Giza.

Back to your circle:
The outer ring contains 33 stones the middle ring contains 26 stones the ratio is 1.269:1...an example of Problem #50 set in a "circular" stone formation.

Just for fun...add the total number of stones...change to degrees of a circle and find the "Tangent" of that number.

Best.
Clive