Halliday & Matthiessen (2014: 270):
Qualitative Attributes are, as noted, realised by nominal groups with Epithet as Head. The Epithet is realised by an adjective (or participial verb form), which is frequently submodified by adverbs of degree such as very, extremely, greatly, including the comparative adverbs as; more, most; less, least; too. The comparatives may be expanded by a standard of comparison introduced by as, than; for. These are either phrases or clauses and are placed after the Head/Thing, in the same position as post-modifying Qualifiers; for example:I think mum’s more upset than he is.Structurally such expressions are Submodifiers within the Epithet rather than Qualifiers; but nominal groups with Epithet as Head may also be constructed with Qualifiers:
Nothing gets past those kids. They’re as sharp as old razor blades.
That’s just tiny, too tiny for words.She’s not very interested in the food.