There are no extra charges for PM, the 37.50 is a minimum Haircut requirement if you have an essentially risk free position like a conversion.
if you look at some portfolio margin examples from CBOE: http://www.cboe.com/micro/margin/margin_req_examples.pdf the fourth line, "Protective Put" with 10 sticks of IBM and 100 puts shows that 37.50 contract minimum margin in play. the margin is $37,500 versus $498,000 under strategy-based margin.
actually, i think that's a good example of the vast difference between the two margin styles, but not a real example of the 37.50 per contract minimum. but you get the gist of it.
yep...what I really like about it is the ability to do short calendars and volatility plays...ie buying the strangle/straddle in low vols and selling the strangle/straddle in high vol's ...another way to leg into IC's...