The rate you see on your Growth account is a weighted average interest rate based on how much digital assets you have in your Growth account. The larger the digital asset balance in your Growth Account, the closer this rate will get to the higher Tier 2 rate.
Example:
For USDC, if the Tier 1 rates were 8.5% APY, Tier 2 rates were 10.0% APY, and the Tier 2 threshold was $100K… this is the blended rate you would expect at different USDC balances:
100,000 USDC Blended rate = 8.50% APY
250,000 USDC Blended rate = 9.40% APY
500,000 USDC Blended rate = 9.70% APY
1,000,000 USDC Blended rate = 9.85% APY