Gravitational field intensity for a uniform spherical distribution of mass is given by:
I=GMr2 for r>>R and I=GMR3r for r<<R.
(a) r1>R and r2>R
I1I2=(GM/r21)GM/r22)=r22r21
(b) r1<R and r2<R
I1I2=(GM/R3)r1(GM/R3)r2=r1r2
(c) r1>R and r2<R
I1I2=(GM/r21)(GM/R3)r2=R3r21r2.