IPA vowels

I'm having quite a bit of trouble figuring out which IPA sounds correspond
with each of the 9 vowels in my conlang... :-( hope somebody can help me
with this since I'll need to give some form of IPA transcription for the
phonological relay! :-)

The main problem is that IPA deals with rounded/unrounded and 4 degrees of
aperture; but vowels in my conlang deal with rounded/unrounded/"stretched"
and only 3 degrees of aperture. Also, front/back-ness tends to be
considered equivalent to the stretchedness by native speakers, leading to
a lot of allophones.

The 9 vowels are arranged in a 3-by-3 tabular format, according to the
roundedness/stretchedness and the degree of aperture: (the following
symbols are *not* IPA transcriptions, they are the orthography)

        rounded         unrounded       stretched
close   u               w               y
mid     o               3               i
open    0               a               e
        (back)          (central)       (front)

I don't know how to describe "stretched" except that it's a kind of
*horizontal* degree of aperture.

Now, as far as IPA sounds go, here's what I'm clear on so far: (SAMPA is
used for the IPA symbols)
        u = /u/         y = /y/
        o = /o/         i = /i/ (possible is /e/ too?)

w is probably /}/, but might also be /2/ ?
The top row vowels, u w y, are what I call "whistling" vowels because they
are highly rounded and sound like whistling :-)

The second row vowels are basically half-open/half-close. 3 is probably
best rendered as /@/ but could also be /3/. I think it's closer to /3/
'cos unlike the schwa sound its articulation is quite deliberate.

The bottom row vowels, 0 a e, are "shouting" vowels because you say them
with your mouth wide open -- especially e which is like a stretched open
front vowel (/a/ ?): pronounced with your mouth as widely as possible both
horizontally and vertically :-)

Anyway, I'd appreciate it if some here who are familiar with the IPA
sounds can help me figure out the "best" IPA transcriptions of these
vowels.


T