Logically I would assume and like it to work you've assumed, but I can't do anything about things not working the way I'd like, so I'm just explaining how they work because you asked, I'm not arguing the logic of them. So since you've asked then I'm assuming that you actually want to ask a question, not argue that your own answer to you question is correct but any other answer is not![]()
I have an ulterior motive in asking these questions: I am implementing a toy brokerage program. This is why I am asking questions about the margin enforcement. Framing these questions as if we were the broker, how could we explain to someone else why the margin requirements? e.g. "Hey guru, the brokerage you run has some unusual margin requirements for seemingly related instruments, how come?"
You need a portfolio margin account. It gives more leverage with SPX options, and also allows cross margining
Clarifying, I am comparing a single long ES future (no option), with the equal exposure SPY short puts and long calls. The expiration is (ideally) exactly one day from now, same as the the settlement time for the Future contract. We should be able to draw a payoff diagram where both portfolios are identical (modulo trading frictions).