There is an alternative way to create the third resonator needed for acute vowels. You will hear the sound in some country singers, a few rock/pop singers and in classical singers of a certain ilk.
Instead of making the third resonator right in the front by the teeth, we create a kind of spoon shape in the middle of the mouth, a cupped tongue-blade right underneath the arch of the hard palate. So the tip of the tongue is not sloping upward and reflecting the sound forwards, but is in fact facing back. The lack of the forward reflector as well as the absence of the hard surface provided by the teeth in the front resonator creates far less of the highest formant, instead making a strong peak at the top of the mid-range. The sharp-edged |ì| is replaced by something like the German umlaut-U sound |ü|. While this can still sound very agressive is pressed quite hard, it never sounds sharp, more like a poke with a broomstick than a stab with a dagger.
When applied to sounds other than the |ì| this technique starts to give a very particular sound which I call 'pinned' where the larynx becomes almost entirely still. There's an article about singing 'pinned' later on.