According to IB, margin requirement of straddle is 21K. For 1 option contract is about 20K. However at C2, with 430K, I can only short 17 spx call. Not mentioning straddle or other option combination. Even without considering straddle, I should have the ability to short 22 spx options. Could somebody change the margin requirement? Espeically for SPX option.
I had this kind of problem as I also trade options, and I had a conversation with Matthew about it last year.
Since C2 tries to accommodate many different brokers, margin requirements are set to be conservative. That way you can guarantee that all subscribers can follow properly but it does mean that your margin availability is more limited than in most real accounts.