Well, I explained the symbols in my previous comment: eɪ is the vowel in FACE, and iː is the vowel in FLEECE. The difference I'm talking about is similar to the difference between the English word "hay" and the English word (well, sort of a word) "hee".
I think what may be happening is that there is a continuum between eɪ and iː, and you and I put the boundary between them in different places. Try pronouncing "hay" but keep going on the vowel (as if you were singing it on a long note), and then gradually change it to "hee", but pay attention to the way your mouth is changing shape internally as you do so; it should gradually close up towards the back.
Now, when the consonant in 黑 becomes more guttural, the mouth cavity has to close up more towards the back in order to do this, so the following vowel becomes more like iː (i.e. hee), whereas in a speaker who doesn't have the guttural "h", the mouth can be more open and hence the vowel remains more like eɪ (i.e. "hay").
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I think what may be happening is that there is a continuum between eɪ and iː, and you and I put the boundary between them in different places. Try pronouncing "hay" but keep going on the vowel (as if you were singing it on a long note), and then gradually change it to "hee", but pay attention to the way your mouth is changing shape internally as you do so; it should gradually close up towards the back.
Now, when the consonant in 黑 becomes more guttural, the mouth cavity has to close up more towards the back in order to do this, so the following vowel becomes more like iː (i.e. hee), whereas in a speaker who doesn't have the guttural "h", the mouth can be more open and hence the vowel remains more like eɪ (i.e. "hay").
I hope this helps somewhat!