When 1 STEEM is 0.50 cent USD than 1 SBD is worth 2 STEEM (= 1 USD).

When 1 STEEM is 4 USD then 1 SBD is worth 0.25 STEEM (= 1 USD).

So 1 SBD is always 1 USD worth of STEEM.

Currently 1 STEEM is 4 USD and 1 SBD should be worth 0.25 STEEM but it's trading higher. 1 SBD is currently worth around 0.9 STEEM ($3.40).

You can't do much with an SBD on the blockchain besides trading it for 1 USD worth of STEEM. So the fact that it's worth more shows that the market doesn't understand the mechanism of the SBD/STEEM relationship.

They are paying $3.70 USD for $1 USD worth of STEEM.