I will give an example. Say, I am a CPO, running client money in a systematic manner. God knows for a very long time it would have been conservative to put on 1 contract for say 15k margin. I keep chugging on, and Feb. 2020 hits. If I was at any other broker, my algo would have continued in it's merry way, and I will make / lose money. But if I was IB's client, trading a decent chunk of money, I have to cut down my contracts by more than 50%, making performance suffer? What am I going to tell my clients? Sorry, I chose a shitty broker?
