Well I have understood you very well and I have used the Kathrein scala calculator to see the coverage this caculator takes the input of the antenna height,V-beamwidth,and tilt and it will give you the range of the main beam, higher beam and lower beam. Yes the priority must be given to tilt to compensate the height of the tower. There are two kinds of tilt Mechanical and electrical. Great mechanical tilts may cause an overlap of neighbor cells of the left side and right side. because the strong signal will hit the ground and then reflects a strong signal to both the left side and right side increasing the overlap of both sides. While Electrical tilts may be better to use to avoid side overlaps. I tried to look for other kinds of antennas with a low gain and low Vertical beam width but all the low gain antennas have high vertical beamwidth. It seems that vertical beamwidth and gain are indirectly propotional to each other. reducing the gain antenna might increase the V-bmw.
“The overlap with the umbrella cell is 100%, whichever is the downtilt you choose for the microcell.”
but we have a lot of microcells close to each other about 100 meter so inorder to make sharp boundaries with minimul overlap so you may use a specific downtilt.