Premium, impact, and the oracle

Why does Hyperliquid measure the premium at an impact notional instead of at the best bid and ask?

• Because the best bid and ask are only updated once an hour
• So that a small order at the top of a thin book cannot set funding by itself
• Because the impact notional is the size most traders use

The impact ask is below the oracle. What sign does the premium have?

• Positive
• Negative
• Zero, because only the bid side counts