The point about stress is interesting. I’ve been playing with pronouncing the phrase, and almost everything tends toward [ɐ] when I speak the syllables one at a time, even the ones I marked with and pronounce as a schwa in normal speech. The notable exceptions are the final schwas in “obstruction” and “onions”, which tend toward [ɪ], and the -nel of “tunnel”, which is something like [nɫ] (vocalic ɫ) ~ [nəɫ].