Babies with a high arch to their palate tend to flick the nipple up into the 'cavity' very easily. There really needs to be so much breast tissue in the baby's mouth that the nipple is forced further back.
There are many ideas and techniques that are used to help in this situation. Experimenting with positioning is important to find the best position for mom and baby. Some moms try sitting the baby beside her so that the chin is on the underside of the breast. Gravity seems to help get more breast tissue in like this. Sometimes mom leaning over the baby works, again with gravity on her side.
Some moms use a modified football hold with the baby wrapped around her hip, facing her side, and baby's lower lip about a half inch under the nipple. She would then position the lower lip on the areola, and wait for the mouth to open wide, then pull the baby on by the shoulders to get a deep latch. Leaning back helps hold baby against her chest.
If this is done right, baby's head will be a little extended, and the latch will be asymmetrical, with more breast tissue over the tongue and less under the palate. The more breast in the mouth, the less the tongue restriction seems to matter, because when the mouth is more full of breast, the tongue has to lift less to press milk out of the breast.
This situation usually gets better with a little time. As baby grows he/she is able to take more breast tissue in the mouth, resulting in a better latch. Many times this seems to spontaneously resolve at around the age of 8 to 10 weeks.