Going to need to get a massive expansion of the HBD float to really tighten the peg. It seems the lack of liquidity is at least one factor in creating too wide a trading range. Having more HBD on the market might help to mitigate that especially since most of the HBD appears to be located on one exchange.
As long as there is protection against massive Hive printing through the conversion mechanism if the price of Hive collapse, then 30% might do the trick to reduce the volatility that still exists in HBD.