Sorry for dissapointing you fellows, but my idea is the correct one!!
What is an antenna pattern? it is the shape of the field strength radiated by the antenna!!
So, Mr. m@u, when we tilt the pattern, the strength will be reduced in the horizon and the radiated power in the cell
that is actually to be covered, increased.
that is because the vertical pattern of an antenna radiates the main energy towards the horizon and only that part of the energy which is radiated below the horizon can be used for the coverage of the sector.
Here, I will answer the question:
Considerable limitation is achieved if the radiated power in the horizon is limited by 6 dB. This means that one can easily predict the smallest efficient tilt angle by simply tilting the vertical radation pattern until the field strength in the horizon is reduced by 6 dB.