Can someone please explain why some securities have "special" margin requirements? I understand that if a security has a 100% margin requirement, it means that the broker sees the security as more risky, thus it wont lend you money to buy it. So does this mean that if a stock only has a 25% initial margin (and a 20% maintenance margin) that the broker sees the security as less risky? I dont see another reason why a broker would let someone get more leveraged than usual on a security unless they viewed that security very favorably. Thus, if they are only requiring a 25% margin, they are saying they REALLY like the stock, compared to one with a regular 50% margin or higher. Is this correct?
I don't know how they calculate it, but I'd say historical volatility and market cap play a big role here.
Could be anything. Market cap, average daily volume, volatility, recent price moves, concentration risk, free float, news and so on and so on.