Question:
Are intrinsic AA values affected by being out of supply?

Answer:
Intrinsic map features are not units, therefore they are not affected by supply; intrinsic AA strengths of units are affected by supply, since they are a component of the unit, which is affected by supply.

The supply rules specify that they affect the abilities of units in movement and combat; there is no mention of it affecting the abilities of map features.

Source:
TEM 67