Martin (1992: 183):
The distinction between internal and external relations, though clear in principle, is in some cases hard to draw, either because it doesn't matter as in [4:15] above, or because certain relations, such as the concessive, are themselves interpersonal enough in orientation that they fudge the distinction being drawn between organising text and constructing field.
 In SFL theory, the distinction between internal and external relations is not the distinction between organising text and constructing field.
In the case of logical relations between clauses, the distinction between internal and external relations is the distinction between the beta clause relating to the enactment of the proposition (interpersonal meaning) of the alpha clause and the beta clause relating to the figure (experiential meaning) that the alpha clause represents (Halliday & Matthiessen 2004: 419). For a semantic perspective on interpersonally oriented sequences (realised by clause complexes), see Halliday & Matthiessen (1999: 123-4).
In the case of temporal conjunction in textual cohesion, the distinction between internal and external relations is the distinction between the temporal unfolding of the discourse (interpersonal time) and the temporal sequence of the processes referred to (experiential time), respectively (Halliday & Matthiessen 2004: 545).
Field, on the other hand, is the ideational dimension of context, the culture viewed as a semiotic system that is realised in language. Field is thus realised by the ideational features of language, including those construals of experience that are logically expanded or cohesively conjuncted by internal and external relations.
The "construction" of field during logogenesis is thus the construal of the ideational dimension of context through the instantiation of the ideational meanings that realise the field.
 Concessive conditional relations between clauses in complexes are logical in metafunction; concessive conditional relations between messages in cohesive conjunction are textual in metafunction. The meanings they realise are distinct from any interpersonal meanings also being realised.