Between October 2007 and March 2008, Interactive Brokers did increase the overnight margin of shorting ES and ER2 options by a factor of 3 to 10 depending on strike price and expiration.
You may be surprised by the margin requirement to short a twenty points out of money ES PUT ( or CALL ) expiring within few weeks via Interactive Brokers.Unless they change the rules recently, it is still very high.
Of course, it is highly unlikely that they will do the same for ES and TF futures.
In the aftermath of the '87, crash, I called my Refco broker and asked them "how they did"? Meaning, how much in the way of customer debits they might be facing? Refco said, "only about $300K, we think" (out of $20 Million company equity). They also said they'd rather customers not trade the SP contract at all (outcry pit, no ES at that time) until things settled down... and if I did want to trade the SP, Refco wanted $50K margin per contract.