Hello,
I dont know about cadence coz I am using mentor graphic, any way might be the same idea
in mentor, when I want to run the AC analyses to find Vo/Vin in DC, I chose the AC signal not the sin signal. the AC signal values are oin dB.
then in the simulation AC setup, there is an option of taking the output node with respect to the AC signal wherever it is found, so the AC simulator in mentor is always takinf the transfer function from the node you want to measure to the node of the AC source