Hypothetical Background: I have an Reg T margin account with Interactive brokers. I have a maintenance margin requirement of ~30% for that; I have calculated the drawdown necessary to get a margin call. Let's say hypothetically I own about ~100k SPY from my savings and ~20k SPY bought from margin debt, and I feel comfortable that I won't get a margin call because I don't think the ~80% market drop I would need to get a margin call is happening anytime soon.
However, I would like to extend my 1.2x leverage without adding more margin. Suppose I buy one E-Mini S&P 500 Future at today's price of about 3695.00; I understand that future would give me 50x leverage on the index. How far would the S&P 500 have to fall to get a margin call on my entire account? I understand the future itself has a maintenance margin, but does this affect my total account margin?