The Boie’nen letter “Ii” symbolizes the pure IPA monophthongal realization as /i/ or /ɪ/:
1. /i/ in "see" or "me" that often is [i]
2. /ɪ/ in "in" or "sit" is [ɪ]
/i/ is often realized as a close front unrounded vowel [i] as in Boie’nen “sibeg” (move back)
/ɪ/ is realized as a near-close near-front unrounded vowel [ɪ] as in Boie’nen “iseg” (fierce or brave);
The diphthong /aɪ/, [ɑɪ] or [ɒɪ] or [aɪ] for American English‘s letter ”Ii” that reflect a more significant change in vowel quality is written in Boie’nen as “ay!” (surprise or shock expressive word).
Note that these American [ɑɪ] phones are more commonly associated with certain accents and are interchangeable.
For example:
1. New York City accent: the /aɪ/ diphthong can be realized as [ɑɪ] or [ɒɪ], with a more back and rounded starting point.
2. Some Southern American English accents: Some Southern accents might also use [ɑɪ] or a similar realization.