Purpose of providing Closer Stirrups Spacing at both Top & Bottom end in RCC Column .Spacing of ties is calculated as per the plastic moment capacity of the column .
The spacing you come up is required at the ends because the moments at the ends is greater and you have most of the cracking going on in the end zones.
To reduce the chance of spalling of concrete we provide better confinement at the ends for a greater ductility and performance. This is the only reason why we have shear ties closer at ends.
And yes, shear remains constant across the column height as the earthquake or wind forces are experienced at story levels and there is no force in between. While the bending moment is maximum at both ends and zero in middle.