Halliday & Matthiessen (1999: 234):
Thus in many instances, not unexpectedly, lexical and grammatical metaphor go together. What we are most likely to be told, after the performance, is that the audience gave thunderous applause. In she felt a flood of relief there is not only the lexical metaphor of flood but also the grammatical metaphor of a flood of relief where intensity is represented as a Thing and the emotion as its Qualifier, contrasting with very relieved, with intensity brought in as Submodifier very to the Epithet relieved.
Similarly, in the example of grammatical metaphor increased responsiveness may be reflected in feeding behaviour there was also the lexical metaphor reflected. But they are not automatically associated, and in most instances of grammatical metaphor, if we reword in a less metaphorical direction, we can retain the same lexical items, merely changing their word class (often with morphological variation, e.g. we act effectively / the effectiveness of our actions).