there is a simple way to keep the posts lined up. i use full shelves and so only need 3 posts and i prefer the triangular ones.
to keep them lined up i drew 3 triangles in marker on the top rim of the kiln walls at about thirds of the way around the kiln. very seldom do i need to put posts outside these marks by more than an inch or two. they are located at the edge of the shelf so i can use every inch of space. after a year or so i re-draw the marks because they do fade over time.
when i get toward the top, i sometimes use a half shelf for leftover small things or to allow a lower shelf to hold something tall on the opposite side of the kiln. still put two of the posts close to the original spot and a centered one on the outside diameter of the half shelf.