No expert, but SEER has to do with efficiency. That is, the amount of cooling produced for the amount of power. Higher the SEER, more cooling for the same power (or same cooling for less power). Airflow is not part of the equation.

However, there is the fact that some units require a different blower to achieve the higher SEER. I would guess that they might call for a variable speed blower which is more expensive than a fixed speed blower.

Basically, air flow rate is more a product of tonnage, not SEER.

average airflow rating is 400 CFMs for each ton of cooling

12 KBTUs=1 ton of cooling.

Understand ductwork has to be sized for both supply and return. Returns usually undersized which leads to poor airflow, poor comfort, and noise issues.

SEER and airflow have nothing to do with the other.

IMO

Thank you for the quick responses.

So in practice do installations actually use the higher flow capability of the air handler for heat pumps?

The manufacturer spec lists air handlers capacity higher than the condenser rating, how much efficiency is lost if coil of the same tonnage rating as the condenser is used for a low end 13 SEER unit? The cross-section of my duct is smaller than the cross-section of the higher tonnage coil.

Larger indoor coils and greater airflow provide greater efficiency for meeting the sensible load. Because of that, those things are preferred in hot, dry climates.

In humid climates, smaller coils and lower airflow are preferred for better humidity removal.