What the blockchain does at 30%:

This should be 20%.
At 20% the chain stops printing hbd and only prints hive.
At 30% the guarantee of 1usd of hive begins to decrease, known as 'the haircut'.

Iirc, at 50% debt ratio you get .6usd of hive.
At 30+% you get some fraction lower than 1.

However, while the price of hbd is below a dollar and above the haircut you can print free hive by swapping to hbd and converting.
It takes 3.5 days, but it's easy hive.
Fairly risk free, too.
A rising price can cut into profits.

In effect this shorts hive with a near certain return of 2 or 3% over 3.5 days, generally.