The water level is mainly for when they first feed, so their first live foods are within reach. As long as you're waterchanging daily, depending on what you feed - ie brineshrimp. You can actually raise the level of the water. What size container/tank are you using and how many do you have?
Any that may start floating constantly or have problems flipping upside down should be separated into containers of lowered water so they don't get so stressed when it comes to eating/floating.