Setting the fan to will raise the relative humidity in the house 10 to
15%. Not a good idea. This is because the water on the indoor coil
and in the drain pan re-evaporates when the compressor shuts off.

The problem is that the surface of the duct is below the dew point of
the air in the attic. This happens when the surface of the duct is
shielded from the attic temperatures by another object, especially when
two supply ducts are in close proximity. air trapped between the ducts
is cooled below the dew point ans drips condensate. The best answer is
to use wide straps to support the ducts so they do not touch each other
or wood trusses or insulation in the attic. I have a formula to find
the surface temperature of the duct somewhere.

Stretch