Vowel is so important. Vowel can help you stabilize your larynx resulting in you reaching the particular pitch you want. You need to narrow your vowel to stabilize your larynx. Try pouting your lips if you can't imagine how to narrow your vowel. Pout your lips and drop your jaw when you sing will help your resonance find it's own place. You need to sing from lower to higher pitch with once voice. Meaning no cracks or breaks in between. Narrowing your vowel is the path to that.
So many vowels in the world. Sometimes different languages have different vowels. For example French got "Û" that English does not. So you can adapt to any vowels on one condition that the audience will still understand the word you sing.
The word "sky" with the vowel /ī/ with a particular pitch might be a problem to you. In this case you can change it to the vowel /u/ like "book" If you're not sure about it, sing it and see if it's understandable and easier to sing.
Right at this point you might want to ask me if there's another to a vowel narrowing apart from comparing from this vocabulary to that vocabulary. The answer is "YES"
Put your thum on one side of your lips and the rest of your fingers on the other side. Squeeze them gently and make sure you don't hurt yourself. Now sing (and drop your jaw also) Those are the exact vowels you need to have. Imagine a fish. How it does to their lips. You will look similar to it but with a more powerful voice. Now when your body is used to having a narrow vowels, you won't need to squeeze your lips like that anymore. Just try to memorize how your lips don't spread to the side but instead drop down. This time you won't look like a fish anymore. You will just look good with a beautiful voice!!!
