Not disagreeing here. Even though it is different from my initial suggestion, I'm happy to see you setting a meaningful rate.
BTW, I'm not that concerned about interest causing a large overvaluation. Once HBD is overvalued at all, the interest is only a very weak incentive to continue to hold it, since you can easily lose much more than the rate by the price going back down to $1. The main reason I would see not to set a higher rate is simply that it is more than necessary to accomplish the goal of attracting enough demand for all of the HBD we are able to supply, given current blockchain rules, while keeping it at or above $1. Any more interest than that is in a sense wasted, but within reason (and 5% or even higher is still within reason), it's a small cost relatively speaking, not a huge concern.
It is certainly not possible to know the exact right number, and we shouldn't get stuck on trying to do so.