A couple points, first is that SBD "peg" to 1 USD is not really backed by anything other than the one week average price of STEEM. So if the price of steem is volatile, then prudence suggest SBD should trade at a discount.

Second, the math is setup so that if >90% is in steem power, it is LOGICAL to power down. If <90% is in steem power it is LOGICAL to power up.

Third, the daily volume is far in excess of the daily powerdown, so while a 10% per day sell pressure is significant, an 80% downturn is an overreaction. However we did have a lot of speculators come in at large volumes when poloniex started trading. Big volumes cut both ways...

Until the poloniex traders have gotten STEEM in their portfolios where they are comfortable, they will likely keep selling so they can chase after the pump of the day.

Until SP is ~90% we will have powerdown sell pressure from the logical whales (most of them). How far? Well that is the big question everyone wants to know the answer to, but cant.

Only time will tell. However, the powerdown volumes will become less and less of a factor as more and more STEEM is created and as some of the whales cancel their powerdowns. But the primary down pressure is from traders liquidating, not power downs as your analysis shows