So are you doing this trade for any reason other than "the last ones worked"?
Being naked short a 1x3 straddle isn't exactly something you want to be doing on a whim....
Lol, so you know what IB's positions are now? More than likely they have a hedge on and are using the exposure fee as a way to pay for the hedge while also allowing clients to keep their positions open if they want.
This reminds me of 2011 when they raised margins of Gold and Silver and people shit a brick.
My guess is short vol./ premium is a bubble trade right now.