The 1.05 threshold isn't set in stone. It was done that way at first to provide a wide safety margin on a new feature and recognizing that HBD was so prone to pumps that even 1.05 would be a huge improvement. The longer HBD stays much closer than $1.05 and the more confidence we have in the mechanism the more likely it is we can tighten the band.
RE: UST: Just Another Centralized Stablecoin