Martin (1992: 517):
…it needs to be kept in mind that in referring to the iconic texts as field-structured, what one is saying is that for this group of texts it is difficult to distinguish genre and field — looking from the perspectives of social process (genre) and activity sequence (field) amounts to very much the same thing (in other words the model of context developing here overdetermines the classification of these text types). With genre-structured texts, on the other hand, the organisation of the text is very different from the organisation of activity sequences to which the text may refer.
 To translate this into SFL theory, the claim here is that there is a text type (register) for which the structure at the level of the semantic stratum is organised according to field (the ideational dimension of context).
 To translate this into SFL theory, the claim here is that, for this text type (register), it is difficult to distinguish between text type (genre) and the ideational context of language (field). One reason why it is difficult to distinguish between text type and context, in Martin's model, is because the model confuses text type (register/genre) with context.
 The reason why "looking from the perspectives of social process (genre) and activity sequence (field) amounts to very much the same thing" is that Martin has redefined genre as field. In SFL theory, social processes fall within the definition of field. Halliday & Matthiessen (2014: 33):
field – what’s going on in the situation: (i) the nature of the social and semiotic activity; and (ii) the domain of experience this activity relates to (the ‘subject matter’ or ‘topic’)The following table clarifies the theoretical inconsistency. In SFL theory, field is located at the intersection of context and system (culture), whereas text type (genre/register) is located at the intersection of semantics and instance type.
The confusion is thus along two scales simultaneously: stratification and instantiation. Moreover, there is a further confounding inconsistency with regard to metafunction, since this discussion is purported to be about mode, the system of the textual metafunction at the level of context.