30% is far too small of an initial margin for such a volatile commodity.

The initial margin is expected to cover a the movement of an observable through making the margin call, the period of time the margin call could be filled, declaring the counter-party in default and closing out the position. This normally adds up to a minimum of 2 working days.

Saying that it's beyond the realms of possibility for bitcoin to jump or fall 30% in 2 days seems ridiculous.