Hi Xavier,
For some security reasons we can not put the antenna on the ground where somebody can reach. So there is no land we can buy there since it is already occupied so the only option is to put on the second floor of the BTSs. I think the best solution is to install this 1800mhz antenna on the 6m monopole and then if the capacity is not enough then we have to split that microcell into two equal parts or reducing it to half of its current coverage.