Experimentally, it appears to me that Interactive Brokers's new volatility exchange traded product margining at least sometimes requires much more margin for a protective call (short underlying + long call) on a long volatility ETP than a long put with the same expiration and strike, even though the exposure is basically the same.
I am a bit surprised by this because IB normally explicitly recognizes a protective call combination and offers pretty good margin for it.
Toonerdy--- I have a similar experience. I am short a number of VXV futures and long 10 VIX 16 calls per future. The maximum loss and therefore margin should be $5k per future. I have excess liquidity of 3 times what the margin SHOULD be-- and yet just moments ago I got an IB general notice that I can't add any volatility trades. I may be looking for a new broker---- suggestions?