Speaking as a partner in the @PolleNation witness, I can tell you that when we discussed how to initially decide our interest rate setting, we both agreed that 20% was perhaps too high. We ended up landing on 15%, because we wanted to set an example of being a bit lower.
But we also know that if we set it too low, it would be too far out of line with the other witnesses and wouldn't actually affect much mathematically but could signal the wrong intentions about our faith in Hive to the stake driven investor constituents of the community.
It would take a very difficult to achieve consensus to get it lower across all the witnesses, but we have tried to set a bit of a precedent with our opting to be one of the lower ones.