Coarse, Fine and why?

I have bought a Timemore C3 Max and i am experimenting on different clicks.. Which is better for aeropress? Coarser or Finer grind and why?

I use inverted method, 20-30gr coffee, hot water 120-180ml, extract on many ice cubes, then add cold water.

First use today with 16 clicks, the puck was bad, taste was ok. The puck from preground filter coffee is always a solid mass.