ATM IV < 16%: 低位，适合入场Low — good entry
16%-20%: 正常水平Normal
> 20%: 偏高，保费贵High — expensive
OTM IV因skew通常比ATM高3-5个百分点。恐慌期IV可能达25-30%+，保费翻倍。
OTM IV is typically 3-5pp higher than ATM due to skew. During panic, IV can reach 25-30%+, doubling premiums.
策略Strategy：等IV回落到16%以下时买入Put，可以用更低的成本获得同样的保护。: Wait for IV to drop below 16% before buying Puts — same protection at lower cost.