Stop large moving objects sticking agiasnt buildings

I have a grid graph with 50 x 50 nodes and node size of 2. There are cube buildings to simulate a street. A (1,1,1) scale capsule can navigate round the corners of buildings fine. The problem I have is when a capsule is any greater then 1,1,1 such as (5,5,5). The collider of that capsule hits against the building stopping it from moving along its path to the end point. I looked into collision diameter and increased it but made no difference to how the capsule collides with the buildings. Erode iterations cant be done as if the number was too high nothing could walk down the street.

Also why isnt Cube a Collider Type for the graph collision class? Say for example you had a tank, surely a cube would be the best colider as if you changed the diameter of a capsule its just a circle.