It also depends on the design ...

It also depends on the design of the cooling tower.  If the tower water cascades from the top and the fan is a forced draught, there will be a lower level of water droplets generated when compared to a tower, which sprays the water at the top of the tower.  Most modern drift eliminators are effective.  If there is no lip at the edge of the unit then water droplets can pass between the eliminators.  Ill fitting drift eliminators will also reduce their effectiveness.  The temperature of the water can also impact the eliminators.  High water temperatures can cause the eliminators to warp and become ineffective if they are the incorrect type.  This is why they should be regularly inspected.