Well tell me where I am wrong.
chance to hit(if >1 then it's 1):= (weapon accuracy)*(received accuracy)*(other modifiers such as vet)
chance to damage:= (chance to hit)*(chance to penetrate)
So as long the chance to hit is not greater than 1, the chance to penetrate is just like any other modifier (when looking at damage)
So for a volks STG vet0 close range against a unit
with 1.5 armour and 1 size -> 0.55*1*(1/1.5) = 0.3685
with 1 armour and 0.67 size -> 0.55*0.67*1 = 0.3685
At first glance your math seems to be correct.
But you seem to miss the point. Certain weapon (mostly hmgs), including the ST44 and bar (don't remember if it applies to Volks ST44 thou) have a variable that allows them to score a sort of "collision hit" on another squad member. If the shot miss the first target it has a chance to hit another target and "reroll".
In some ways it make sense for squad with small number of entities to have this advantage since their member get hit by multiple enemy entities but in some case like the bar or the Kubel it should have been removed.
In you example the chance for both "rolls" to miss would be around 40% (or chance to hit would around 60%) that the ST44 would worse vs the unit with armor.
Hope that I explain clearly enough.