It is not about the antenna, but rather the frequency band of the antenna ! You can find the formula here :
relation : Free space loss
you’ll see that 900MHz provides twice more rx power at the same distance (twice the power = +3dB).
Furthermore, 900MHz tends to get less attenuation from obstacles (such as buildings, windows, trees, etc.), so it covers further away.
relation : Okumura Hata, Radio propagation, etc…