Vowel /ɪ/ is spelled <i> or <e> in beheaded and courses. The /eə/ diphthong is <air>, <are>, <ear> in swear, or <ar> in Sarah.
The contrast is not a problem for any known group of learners.
Interesting pairs include:
beheaded bareheaded
filly fairly
sirrah Sarah
The mean density is very low 0.1%. The list makes 27 semantic contrast, giving a high loading of 93%.
beheaded bareheaded bid bared Billy barely bin bairn bins bairns biz bares chid chaired courses corsairs did dared dint daren't filly fairly finis fairness fizz fairs hid hared his hairs his hares id aired is airs kid cared kin cairn lid laird lids lairds Liz lairs Ms mares sirrah Sarah skid scared squid squared swiz swears whiz wares
Credit: John Higgins