The /ɔ/ vowel is usually spelled <or> but we also see <our> and <au> and <aur>. The schwa is most often spelled <er>, but we also see <a> and <o> in cos (the weak form of because pronounced /kəz/). Not listed in this dictionary with both pronunciations, the strong and weak forms of for, /fɔ/and /fə/ also make a minimal pair. The homograph discourse turns up here contrasted with discus, having been in another list with different stress in the pair discourse/discuss. Notice also how the homographs consort and concert actually make minimal pairs both as two nouns and as two verbs.
This contrast between a long vowel and the schwa is unlikely to cause problems since the schwa is always unstressed.
The list has a number of polysyllable pairs, where the contrast occurs on a syllable either unstressed or carrying secondary stress, including:
audition addition
centaur centre
concord conquered
exorcise exercise
The density figure is trivially small at 0.45%. The set makes 12 semantic contrasts giving a loading of 57.1%.
audition addition auditions additions awe a cantor canter cantors canters cause cos centaur centre centaurs centres concord conquered conformation confirmation conformations confirmations consort concert consorts concerts discourse discus discourses discuses exorcize exercise exorcized exercised exorcizes exercises exorcizing exercising haulm h'm lessor lesser
John Higgins, Shaftesbury, December 2009