It's probably noteworthy that a different strain of thought about necessary ratios does not look at friendly / allied forces, but at friendly forces / frontage in kilometres.

This was often done in regard to breakthrough battles (guns/km, tanks/km, AT weapons/km) and there were also rules of thumb about acceptable frontages for battalions or brigades (of specific type, such as mechanized infantry) in various forms of combat (attack, defence, delay).

The latter seems to have been favoured for scenarios with unusual force densities (such as the Cold War when 26 NATO divisions were supposed to defend a 1,000 km front line - this took rather 50+ divisions in WW2).