Left side of south spawn, back at the cutoff. As soon as it was noticed, smoke mortar, call in arty and major arty made very swift work of it. I'm talking seconds not minutes. There were undoubtedly things I could have done differently but none which were objectively more correct without benefit of hindsight.
So the cut off on the right side, behind the house on the middle, behind the train line, in front of the train line behind the fuel point ?
Rails and metal plays with both side having a half of the map and slowly creeping or you constantly swap between the 2. If you put the Schwerer on any side, this means you are playing for the first.
That's absolutely your mistake (and you are relying for emergency def in your partner) if both armies can't stop a major from running into your position, dropping 2x offmap into it cause your whole army is supposed to be fighting from that side with small incursions from your positions into the left side. If you have the left side and fightings towards the right, it's your fault if you put the Schwerer in any side besides your base as you are extending the frontline in such a way that it's irrelevant that you call a "strat" point a cutoff as it's way more vulnerable than it would supposed to be if you had the other side.
USF: armor (RNG bombs), infantry and the other 2 offmap requires a unit to get nearby.
SU: IL2 /AT nade bombing
UKF: Precision barrage, concentrated barrage
Check what commanders they have on the loadout. Anytime you play OKW, you should know that you can have your trucks been late game nuke by 1.5 offmaps if they have any of the above. That's not hindsight, that's knowledge and experience.
Same way if you are facing, say Penal spam (satchel rush) or late game Hammer (with gammon bombs). If the enemy can have a straight LoS into the Schwerer, then it's not in a defensive position.