Martin (1992: 417):
The interpretation of grammatical metaphor as a processing interface opens up the question of what the interface is for. This can be answered from above, with respect to register variation — interpersonal metaphor is sensitive to tenor, ideational metaphor to mode. The relationship between field, mode and tenor and grammatical metaphor will be taken up in Chapter 7 below. Here the problem of interfacing will be approached from below by asking questions about the function of packaging information as Theme, New, Subject and experiential clause and group functions.
 No argument has been presented that justifies the interpretation of grammatical metaphor as a processing interface between discourse semantics and lexicogrammar, it has merely been asserted (op. cit.:401). The interpretation derives from confusing realisation with instantiation; see the explanatory critique Misrepresenting Grammatical Metaphor here.
 To view grammatical metaphor — construed as a processing interface between discourse semantics and lexicogrammar — from above is to view it from discourse semantics, not from context (field, tenor and mode). In SFL theory, grammatical metaphor is an incongruent relation between semantics (meaning) and lexicogrammar (wording), and viewing it from above means viewing it from semantics.
 This misconstrues context (field, tenor and mode) as register. Context is the culture construed as a semiotic system; it is more symbolically abstract than language. Each register, on the other hand, is a variant sub-potential of language itself; register variation is a point on the cline of instantiation between system (language) and instance (text). That is, the confusion here is between stratification and instantiation. No argument has been presented for the interpretation of context (culture) as register (language); it has merely been continually asserted.
 To view grammatical metaphor from below is to view it in terms of its lexicogrammatical realisations. To consider the function of these metaphorical realisations is to view grammatical metaphor from above.
 To be clear, grammatical metaphor provides alternative groupings of quanta of information, such that meanings are realised as alternative wordings to the congruent, potentially at all ranks.