The group MG/r occurring in an equation indicates that action at a distance is being described. Newton realized that something unknown must be operating on a smaller scale, but had no tools to explore it. Einstein offered geometry of curvature which can be expressed locally. but G/c2 remained invariant in General Relativity as shown in the integration of functions.
Einstein offered a variable scalar light speed when gravity must be considered.
c/co = ( 1 - 2MG/rc2)
Suggesting
G/Go = ( 1 - 2MG/rc2)2
By applying equivalence principle for mechanical acceleration and making r very large
c/co = ( 1 + v2/c2)
which is just a case of invariant h Planck's constant, but results in G/c2 that decreases very slightly with increasing speed. Then one possibility of G is given,
G/Go = ( 1 + v2/c2)2
but this result is not in agreement with Vacuum Partition theory.
General relativity seems to be over constrained except in the low energy case.
Einstein's ( c/co = ( 1 - 2MG/rc2) ) is not exactly compatible with invariant (G/c2).
How Is Large Scale Gravity G Expressed In Local Properties Of Space?