Halliday And Matthiessen (2014: 676):
Like expansion, projection is manifested both logically and experientially within the ideational metafunction; but outside the ideational domain, it is manifested interpersonally rather than textually, thus contrasting with the textual manifestation of expansion: see Table 10-5.
That is, while there are conjunctions marking rhetorical relations of elaboration, extension and enhancement, there are no conjunctions marking relations of quoting or reporting; and while there are interpersonal resources for realising projection (e.g. allegedly ‘they allege’; probably ‘I think’), there are no interpersonal Adjuncts or other interpersonal manifestations of expansion. There is thus a significant difference between expansion and projection.