Vowel /ɪ/ is here spelled <i>. The /ʊə/ diphthong is <oor>, <our> or <ure>. This dictionary has /bʊən/ as the only pronunciation of bourn (meaning stream or boundary). Other dictionaries give that as an alternative to /bɔn/, which would make the word a homophone of born, reducing the number of minimal pairs to 5.
The contrast is not a problem for any known group of learners.
The mean density is insignifcant at 0%. There are 6 semantic distinctions, making for a loading of 86%, or 100% if bourn is excluded.bin bourn bins bourns biz boors lid lured Liz lures mid moored Ms MoorsGeographical: Outside English-speaking countries, most visitors are from Yemen, Hong Kong, India, Nigeria, Spain and Malaysia. Average 5 visitors per month.
John Higgins, Shaftesbury, January 2011