These are both short vowels and both are common in unstressed positions. Indeed the schwa hardly ever carries stress. Confusions occur even among native speakers. Many of the pairs contrast the -es inflexion with agent plurals such as arches/archers. In some cases I am not sure if a distinction would be made consistently, as in affect/effect, palette/palate and precede/proceed, for instance.
Interesting pairs include:
Since both sounds are frequent in the language as a whole, the mean density is low at 1.1%. The number of semantic contrasts is 316, giving a high loading of 87%.
accuses accusers adulteress adulterous adulteries adulterers adventuress adventurous advertises advertisers advises advisers Ali Allah ammeter amateur ammeters amateurs Annie anna announces announcers arches archers army amah armies amahs armouries armourers assesses assessors atomizes atomizers avenges avengers badges badgers banted bantered batted battered belly Bella besieges besiegers betted bettered bibliographies bibliographers biographies biographers bizarre bazaar blazes blazers bleaches bleachers boarded bordered boozes boozers botches botchers boxes boxers bruises bruisers buggies buggers bulldozes bulldozers busted bustard butted buttered buzzes buzzers cadges cadgers canny canna canted cantered catches catchers challenges challengers charges chargers charted chartered chases chasers chatted chattered chokeys chokers cities sitters cleanses cleansers clinches clinchers coffees coffers collies cholers colonizes colonizers comfit comfort comfits comforts composes composers compresses compressors condenses condensers confesses confessors Consett concert conveyances conveyancers cookies cookers coolies coolers copied coppered copies coppers counted countered counties counters courses coursers covet covert covets coverts covey cover coveys covers crony krona cross-benches cross-benchers cruises cruisers dances dancers deliveries deliverers Devizes divisors dickeys dickers discomfit discomfort discomfits discomforts discoveries discoverers dispenses dispensers dodges dodgers dollies dollars dory Dora dosses dossers doted dotard douses dowsers dredges dredgers dresses dressers edition addition editions additions educe adduce educed adduced educes adduces educing adducing eerie era effect affect effected affected effecting affecting effects affects elide allied elude allude eluded alluded eludes alludes eluding alluding elusive allusive emend amend emended amended emending amending emends amends emission omission emissions omissions emit omit emits omits 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hyperbole hyperbola hyperboles hyperbolas idolatress idolatrous illusion allusion illusions allusions imminence immanence imminent immanent in 'un incises incisors indexes indexers instillation installation instillations installations Jeanie Gina Joanie Jonah juries jurors kepis capers kisses kissers lackeys lacquers laddies ladders lances lancers launches launchers lazes lasers ledges ledgers lighted lightered liquidizes liquidizers lodges lodgers loses losers lounges loungers lurches lurchers manages managers Marches marchers mashes mashers matted mattered mazes masers medleys meddlers mercies mercers merges mergers minces mincers miry Myra mixes mixers moated motored moulded mouldered movies movers mummies mummers murderess murderous nattily Natalie offices officers oppresses oppressors organizes organizers palette palate palettes palates palmy Parma parky parka parleys parlours parry para pasty pasta patted pattered patties patters perishes perishers perjuries perjurers 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resonated revises revisers rises risers risky Risca rushy Russia sallied salad satin Saturn sauces saucers scavenges scavengers scented centred scorches scorchers scrounges scroungers searches searchers seduces seducers seizes Caesars silences silencers silly Scylla sillies Scyllas sketches sketchers skirmishes skirmishers smashes smashers snatches snatchers Sophie sofa sorceries sorcerers spatted spattered splices splicers sponges spongers squeezes squeezers stabilizes stabilizers stages stagers starlit starlet steeplechases steeplechasers stretches stretchers successes successors summit summat Sundays sunders supervises supervisors suppresses suppressors surplice surplus surplices surpluses sympathizes sympathizers talkies talkers tatted tattered teaches teachers teases teasers teeny Tina tellies tellers tended tendered thatches thatchers threshes threshers timpani tympana topis topers torches tortures totted tottered tourneys turners traces tracers traduces traducers tranquilizes tranquillizers transgresses transgressors treasuries treasurers trenches trenchers trespasses trespassers twitted twittered uses users verges vergers villages villagers vouches vouchers voyages voyagers wages wagers Wally wallah washes washers watches watchers welshes welshers whiskeys whiskers withies withers womanizes womanizers yogi yoga
Credit: John Higgins