OP_CSV requires that the transaction spending this UTXO have an nSequence equal to or greater than the value in OP_CSV.
So if the UTXO with OP_CSV created 100 blocks ago and set the relative timelock for only 20 blocks, and now I want to spend this UTXO, I need to set the nSequence to 20 blocks, so finally the timelock will be 120 blocks.
Is it correct?
If yes, this means that most of the time the relative timelock is greater than the set value, unless you spent the UTXO in the next block after its creation.