In LPD, for the word sequel the given phonemic transcription is ˈsiːk wəl, which indicates that the vowel /iː/ should be fortis-clipped by k.
However, the pronunciation heard on the CD which comes with the book is clearly [ˈsiː]+[kwəl], which shows no clipping at all, as the k does not belong to the first syllable, being the onset of the second syllable.
No, I can’t, beyond reiterating that speakers are not consistent in whether or not they reflect these boundaries in their pronunciation, and that there are considerable differences between different speakers and different accents. All I know is that when I say this word myself, I believe that I normally do have fortis clipping of the iː. I have no idea why the actor who recorded the word in the studio on the occasion in question appears to have pronounced it as if it were a compound such as sea quest. And if I had shown sequel in the dictionary as ˈsiː kwəl, as you imply I ought to have done, you can bet your bottom dollar that the actor would have chosen to say ˈsiːk wəl, as I do, and you would still be complaining.
Further, as there are a large number of words for which the phonemic syllables (based on a number of syllabification principles) do not align with the phonetic syllables (an example is Sundridge ˈsʌndr ɪdʒ phonemically, but [ˈsʌn] +[drɪdʒ] phonetically), it seems that from an ESF perspective, a phonetic transcription which stipulates the phonetic syllables would be of great help to foreign students. It would be a godsend if such a dictionary were made available.
Actually, Sundridge, the name of a village in Kent, is a particularly interesting case. All three possible syllabifications ˈsʌndr ɪdʒ, ˈsʌn drɪdʒ, ˈsʌnd rɪdʒ are phonotactically well-formed (if you accept my argument in favour of recognizing syllable-final (n)tr, (n)dr, as in ent’r a plea, und’r a cloud). The etymological one is the first: the name comes from OE sundor ‘separate’, cognate with the stem of modern asunder, plus an element ersc ‘ploughed field’, which is also to be found in the name Winnersh (a place near Reading). Popular etymology, though, might seem to favour the the second, as if it were a compound of sun, or the third, as if it were ‘ridge of the Sund’. My choice was of course the first, just as in sundry, which following my general principles I syllabify as ˈsʌndr i.
I repeat that speakers (and accents) differ widely in the extent to which they make these boundaries audible in their speech and in what articulatory means they employ to do so.
I’m afraid, Jacob, that as things are you have to choose between my LPD, where I at least try to supply a syllabification that predicts the likely boundary-adjacent allophones in accents like mine as accurately as I know how, and Peter Roach’s EPD/CPD, which divides syllables entirely on phonotactic grounds, making no claim about boundary-adjacent allophones. If you think there’s a gap in the market for a third approach, do feel free to try and fill it. Peter and I have done our best.