In SPWWII the ratio should be about 1:1,5. Against an opponent with substancially lower skills and/or lower experience even 1:1 could work out sometimes in SPWWII.
In SPMBT it's a completely different story. The more recent the battle, the more the advantage goes to the side of the defender. AP-arty, ATGM, vis40, better fire control, higher difference in the cost between AFVs and infantry, better AT capability of infantry all play into the pocket of the defender. I guess that was seen in the Final Armageddon first round as well:cheeky:.
But in SPWWII the AFVs are relatively cheap, only few infantry squads are capable of destroying AFVs from the distance of two hexes or more and smoke can be used very efficiently. All this enables the attacker to operate very efficiently with mech assault using overwhelming superiority in breakthrough points. A defender without CD (=range filter) is in a world of trouble...
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Thexder