The point is that in the post payout calculation, the blockchain does not consider the current price of STEEM DOLLARS. It assumes 1 SBD is always about equal to 1 USD, and issues an amount of SBD based on that.
Regarding the amount of STEEM you receive, when STEEM was worth 10 cents in SBD, 1 SBD = 10 STEEM. Currently, on the STEEM Market, 1 SBD = 1.41 STEEM. Meanwhile, coinmarketcap currently shows 1 STEEM = $2.16 USD.
And, if the blockchain's giving you more SBD than it realizes it's worth, that's where the extra STEEM comes from. But of course, if you're converting with STEEM over $2 USD versus when it was a much lower price, that's likely why you feel you're getting less STEEM for your SBD.
At the time I converted, SBD was close to $2 USD and Steem was just above $2 USD. The spread is slightly greater now, but that shouldn't reverse the rates. This is what is totally confusing to me. It was only a week ago or so that I made the conversion.
And that is why I believe that if the price of STEEM goes up, earnings in SBD will be worth less and less as far as converting them to Steem and earning vests (unless the amount of SBD earned keeps up with the value of Steem).