How does the glottis affect stress and unstress sounds in English?

[fxdung]

Is that correct: in stress sound the glostis is more open and in unstress sound the glostis more narrow?

 

[phinds]

Is that correct: in stress sound the glostis is more open and in unstress sound the glostis more narrow?

What research have you done to find the answer? What have you found?

 

[fxdung]

I am very difficult to hear unstress sounds in English. I guess unstress sounds is made when glotis is more narrow.