Inside the vault tiers, $TKR APY may vary depending on the mining power. The more participants join the platform, the less the mining power becomes. This is designed to reward early adopters of the ecosystem. This is separate from the USDT yield distribution and does not affect your USDT APY.
The platform communicates variability based on participation rather than promising a single fixed $TKR APY. The APY is dynamic and it decreases over time as the ecosystem growths.