Here was the reply I got in PM from ids. Exactly answered my needs, maybe some others could benefit from the same. This applies only to short positions, where they're treated differently than longs.
The list on the Web page has non-marginable securities. Your securities are marginable. If you go long, the margin will be 15% or so. The problem is you are shorting and market capitalization of these funds is below $500 million. We consider such positions as dangerous. The margin goes up linearly from nominal to 100% for market cap moving from $500 to $250 million. We are using multi-days moving averages of market cap but you can recon the margin approximately. Now, below $250 you can get more than 100% margin if it is a cheap stock (less than $2.5). I hope it makes things clearer for you.