You can earn more UNIC by staking UNIC (converting into xUNIC).
APY will fluctuate on price, fees (which come from volume) + who enters and exits the pools - it's not a fixed number.
0.05% of all volume on Unicly is taken as fees, and are periodically used to buy UNIC. This UNIC is distributed to the xUNIC pool, making the UNIC:xUNIC ratio go up over time. xUNIC doesn't earn yield block by block, since this conversion is made periodically.
It follows the exact same model as SUSHI and xSUSHI: https://help.sushidocs.com/products/sushiswap-staking-sushibar-xsushi