Martin (1992: 314):
As far as analysing lexical cohesion with specific fields in mind is concerned, all of the elaborating structures discussed above can be taken as realising single message parts. This is the main source of incongruence between message part and lexical item as these units are being defined here.
 In SFL theory, field specificity is irrelevant for analysing lexical cohesion — as it is for all non-structural resources of the textual metafunction in the grammar.
 As demonstrated in recent posts (since 10/10/15), many of the 'elaborating structures' did not involve elaboration, and genuine elaboration relations were misclassified as extension or enhancement.
 In SFL theory, 'incongruence' is a technical term that refers to a metaphorical relation between the two levels of content, semantics and lexicogrammar. Here it is applied to a non-metaphorical (congruent) relation between a proposed experiential unit at the level of (discourse) semantics, and the output of the most delicate systems of the lexicogrammar.