This week, I paid more attention to my body posture as I practiced and I noticed that allowing more flexibility for my articulators helped me get closer to my archetype's pronunciation. Faster jaw movement, lip spreading and tongue movement played a big role in improving my pronunciation. I read the article on "vowels of North American English" and this was such a useful resource for me this week because it clearly described the postures for lax and tense vowels.
Listening to my latest recording gives me much hope that I can actually improve my pronunciation. Practicing consistently and repeatedly while paying attention to single words or phrases turned out to be so helpful. Deliberate practice indeed works! I am convinced I will improve more over time.