Ok, ​let me explain you the reward system.

If you get 10 USD from a post-it​ gets split up 50-50 by SBD to SP ratio you get SP at the rate of STEEM.

For example, ​if STEEM is 5 USD then​ you will get 5 SP for a 10 USD post and the other half you will get in SBD.

Now Since SBD is pegged to be at 1 USD at all times the system treats​ it as 1 USD and we get 5 SBD for a 10 USD post.

I will try to make a post to better explain it.