The gain of the antenna only tells the relationship of the max radiation vs the average radiation.
Given 2 antennas have the same efficiency and the product orientation is such that the maximum gain is in the direction of the communication link range will be longer for the 3dBi antenna. Given this increase at transmitter the range will be 40% longer. Increasing the gain on receiver will adjust the range with similar, given that the link range is not limited by background noise.
Last Update: August 8, 2017