Black holes decrease as they evaporate and their radius decreases as well.
So what is with a cosmological horizon?
If cosmological horizon is just a black hole centered at the opposite side of the universe, we should see the radius of the external space groving as the radius of the BH decreases.
But if the radiation decreases the horizon entropy we should see the area of the horizon decreasing.
What is the correct conclusion?
I think there's a misinterpretation here that's causing your confusion. There's a difference between the event horizon of a black hole and the cosmological horizon.
The event horizon of a black hole is the place inside which nothing can escape from the black hole. The cosmological horizon, on the other hand, is the place beyond which an observer cannot "retrieve information." The difference between the two is basically that the event horizon of a black hole is in the same place for observers in different locations, while the cosmological horizon differs for observers in different locations.
Also, if the cosmological horizon was the edge of a black hole, the black hole would have to be centered right where we are - which is highly unlikely!
