The soul that has attained Paramapadam is in an exalted position. That does not expect our tharpanam at all. That soul eternally experiences divine Supreme bliss. The Vedas are very lucid about this as can be seen from Chandogya Upanishad.
Notes
We perform tharpanam for them because this is ordained by the dharma shastras and the Vedas. They are not going to be satisfied by our tharpanam. If we do not follow the duties prescribed by the dharma shastras and the Vedas, we beget sin. Instead of being concerned about the souls that have attained Paramapadam, we must be concerned about our status and must perform as ordered by the scriptures and to satisfy the Paramatma who is the antaryAmi in the departed souls.
As scriptures are the cause for actions and inactions, it is sufficient we follow its rules, and the departed souls and Perumal are not deprived of anything.
For example, if we stop doing tiruvaradhanam for our household Perumal, He does not lose anything.
If we continue to do trivaradhanam, it is us who benefit and not Him. This explanation is applicable for this query as well.

