To merge, or not to merge?

I'm SO confused! I thought I understood this vowel merger business but not I'm not so sure. I thought the/aw/ and /ah/ sound were merging into
/ah/ but in fact it looks like they merge into this other damned vowel somewhere inbetween (which is represented phonetically as a symbol I can't create on this computer).

ANYWAY...I wrote a desparate email to Dr. F, my prof., asking to please clarify this /aw/ ~ /ah/ merger thing. I'm almost finished... if I could clear this up I could print and do all the final touches. Arrrrgghh!!