From what I know: matrix parameters are designed to represent a kind of "dimensions" or "aspects" within an information space to allow to reference a resource that is difficult to represent within a hierarchy. Because of this design purpose, matrix parameters may appear anywhere in query path, so that you can define an URI

/employee;status=active;occupation=developer;/issues;status=assigned;/

that represents a "multidimensional" resource where each part of path can have different interpretation with respect of its own matrix parameters.