Update SPOT BondIssuer Tranche Ratios to [33/67]

Short Description

Proposal to update the tranche ratio parameters in Spot's BondIssuer from [A/Z] = [25/75] to [A/Z] = [33/67]

Proposal Details

The tranche ratios balance safety with capital efficiency.

Increasing the A ratio from 25 to 33 means:

• With 100 AMPL, one could mint 33 SPOT instead of 25
• For A tranches to be negatively impacted, AMPL supply* would need to decrease by only 67% instead of 75%, over the course of the 28 day bond.

* Note: "supply", not "Market Cap"

Decreasing the Z ratio from 75 to 67 means:

• Z tranche rebase multiplier increases from 1.33x to 1.5x (multiplier = 1 + A / Z)
• Higher Z tranche multiplier means higher effective multiplier on the Rotation Vault
• Rotation vault can sustain a higher SPOT supply for a given TVL size

To read more on Spot's configuration, see About SPOT Configurations in the docs.

SPOT has been live for just over a year. It was launched with a conservative configuration of [20/80], with the assumption that it would be relaxed over time. Last May, it was updated to [25/75].

The most AMPL supply has contracted within 28 days, since the Sigmoid rebase curve was instated on March 26th 2022, is 40%.

It's also worth noting that the rebase multiplier of the Rotation Vault would not change instantaneously with this update. It would rotate in slowly over the course of a month as new bonds come into the system and old bonds leave the system.