y_vel#=y_vel#+1/((EntityY#(Player)-PickedY())^2/.75)
How about this? Of course, no fan is realisticly going to lift a person unless specially designed with a wind tunnel, so you can't really say that a fan is realistic. Anyway, this is a fan that has exponentially less effect farther away, giving more realism. Change the ".75" to modify the fan velocity and fiddle with the "1" for the overall amplitude.