I sometimes have to sing songs at the very edge of the top of my vocal range. I have a number of techniques to do this but when I'm singing blues or American Oldtime I sometimes use a folk song technique where I move the rear of my tongue up towards my soft palate. For some reason, this makes it easier to hit my high notes than my regular voice.
Why is this?
Note that this is not the "head voice" technique which you can feel resonate behind your nose. With this technique, the voice appears to resonate towards the back of your palate.