Procedural textures, by default, are computed relative to the minimum extent of each element, or to the origin of its cell, if any. Where a model is constructed from a number of separate surfaces, then these should be grouped, before applying a procedural texture.

A simple way to do this is to create a cell of the required surfaces. They will then be processed as a single element.

If left ungrouped, the procedural texture is applied relative to the origin of each surface individually. In other words, there would most likely be mismatches of the texture at any edges.