I have a couple of students whose /I/ vowels are a mess. Either the tongue is curling toward a consonant, or never makes it high enough to give the vowel any clarity.
This seems to be an endemic issue amongst people who grew up in Saint Louis.
So, to fix this issue, these students practice on these words, sustaining the tone and focusing on keeping the tongue still:
The vowel on each of these should be exactly the same!