I've been trading in ES options for a while now and have had no issues with it.
For some reason I now find myself in a position to switch to SPX options\* and in my initial, shallow experiment I noticed that selling an SPX option attracts way higher margin than when selling 2x ES options (1 lot SPX = 2 lots ES)
when selling a PUT option at the same strike, same expiry, 1x SPX option charges $80K margin, while 2x ES options charge only $60K margin. In another instance, SPX charges almost twice the margin compared to 2x ES.
Is this what many of you have experienced as well?
\*for those interested in why I'm switching to SPX options - the broker accepts the asset I own (an ETF) as collateral with about a 15% haircut, but only if I trade in SPX options. Anything futures/futures options - I need to maintain cash balance, no collateral allowed.