Sorry, looks like it was operator error!
I misinterpreted the line I was looking at. I was focused on the bottom line "total requirement", which combines the actual SPAN risk parameter + "net option value" (the amount of cash I'd theoretically have if I was selling these deep ITM calls today).
The SPAN risk parameter, the top line in the report, is actually correct in both synthetic and actual put cases.
I misinterpreted the line I was looking at. I was focused on the bottom line "total requirement", which combines the actual SPAN risk parameter + "net option value" (the amount of cash I'd theoretically have if I was selling these deep ITM calls today).
The SPAN risk parameter, the top line in the report, is actually correct in both synthetic and actual put cases.