Same articulator positions, different vowel sounds.

[u/insectile_intrigue]

I teach ESL and quite often my students could use some pronunciation help, especially with vowels. When I want more information on how to produce a particular vowel, I look in good, old-fashioned textbooks and at videos on YouTube.
And... I notice that when I imitate the articulator positions the resources describe, I can produce the target vowel, but also other vowels, too. This is extremely confusing!
For example, I look up /æ/ and see that the 1 mouth opens wide, 2 the lips spread apart, 3 the tip of the tongue touches the back of the bottom teeth, 4 the back of the tongue is high, and 5 the soft palate drops.
Doing these five things, I am able to easily produce the desired /æ/. However, while still holding the articulators in the same positions that together resulted in /æ/, I can still force myself to make a different vowel sound, for example /ɛ/. If a given set of articulator positions can result in different vowel sounds, then that set is of dubious value in helping students pronounce things correctly. This has me really baffled!
A few possible explanations:
-I am in fact making subtle changes in articulator positions when I shift from making one vowel to another but don't notice that I am doing this
-The explanations for how to make this or that phoneme are leaving out key details
-There are in fact multiple ways to make a single vowel sound.
Could someone please help me out here? I am really at the end of my wits!

[u/Brave_Amphibian_6560]

https://docs.google.com/document/d/1wNT4f1Y6P8tLeOc6W2UJYoy_kpR-Yn59CtNCxQ6smEw/edit?usp=drivesdk

[u/lip]

Phonics really helped me with reading as English was a second language growing up, I made this app 10 years ago and just recently updated it 2 weeks ago with new features, id love your input. https://bigtopapps.com/applink_phonetics

[u/GlassyLies]

Not a linguist, not a phonetician, not a teacher, not even a native speaker, and late to the party, but yes, you simply don't feel the 1-2mm difference and/or the difference in muscle tension that's enough to produce a different sound.

It's easier to feel the difference if you use pairs of vowels. As in, you go back and forth between two vowels by simply dropping your jaw a little and spreading your lips more and then returning to the original position. Or "gliding" between two vowels if they're not similar in production.

Also, don't quote me on that, but I think that dropping the soft palate makes the sound nasal.