Halliday & Matthiessen (2014: 500):
Like elaborating clauses, enhancing clauses of this type may have some premodifying element as their strict semantic domain, typically either Numerative or Epithet in a nominal group or an intensifying Premodifier in an adverbial group; these are clauses of comparison and result used in comparative constructions, e.g.
I’m as certain of it [[ × as if his name were written all over his face ]]
The actual formation of shale is somewhat more complex [[ × than indicated in Table 4-3]] .
Another survivor, soaked, wide-eyed with shock and too distressed [[ × to give his name]] , said ‘We were having a wonderful time when it turned into a nightmare.’
Within the vortex, temperatures become cold enough [[ × to form stratospheric ice crystals]] .
Then he told us anecdotes of how he had gone across the Channel when it was so rough [[ × that the passengers had to be tied into their berths, and he and the captain were the only two living souls on board who were not ill]] .
The embedded clauses relate respectively to [the underlined Premodifiers]. Again, however, there is no need to represent this relationship in terms of a different structure.