When using 3 rings I always put 2 in the front to support the scope with the scope turret pressed tightly forward against the middle ring. The reason for this is that the upward force of recoil is like a rotating fulcrum with the pivot point being your wrist. The farther from the pivot point the more force so the front of the scope is subject to the most stress. Also the rearward force of the recoil combined with the rotating upward force will cause the scope to creep forward. The mid ring tight against the front of the turret will prevent that. This also makes the case for a rearward mounted scope as it imparts less stress on the scope than a more forward mounted one.
I also agree that if 4 fit go 2 and 2. The 4th ring is cheap insurance.
"Therefore go and make disciples of all nations,... "
Handgun hunter since 1979 - haven't used a rifle since!
HHI member #992, NRA, SCI.