Why are towers biased?

Towers shoot at me when 10 of my minions are on it and I enter after they are already occupying the tower. Is that normal?

Enemies chase me behind our tower with none of their minions in sight and it doesn't fire at them at all. Sometimes after they start running away it will fire and hit them once and scratch them. Is that normal?

I notice other players when they are shot at by towers the timing between shots is slow enough that if it fires once and they run away they don't get shot again. When I am in the same situation and run within the same range they were, the tower is able to get off 3 shots at me in the time it takes to get one shot off to other players. Is that normal?

Why are the towers discriminating against me in this game?