Most people naturally assume that tower coverage is omnidirectional, a big circular radius with the tower at the center. They wonder why towers aren't spaced out better on maps.
This is rarely the case. The tower is usually covered in directional antennae, some with narrow or confined arcs and some with wider arcs, some with lower power and some with higher power, some are physically higher or lower on the tower (or just unfortunately adjacent to loud neighbours) which affects their performance significantly. Often, the tower itself isn't owned by any carriers, they just rent antenna space on it, it's covered with all sorts of other radio and radar junk, the more densely populated the signal traffic the higher the electromagnetic noise floor, harmonics and parasitics and transients have a nasty tendency to multiply onto each other. Towers also come in a variety of heights and forms, lol.
And of course there's obstacles, buildings, artificial and natural terrain features, electrical and magnetic anomalies, they all influence where antenna coverage should (and should not) be directed. Electrical utilities are costly, perhaps even moreso on an island, so transmission power is kept near the minimum needed to provide "acceptable" quality of service at all times (perhaps fluctuating along with demand, perhaps not).
