DO NOT Cut Lip-Seal Flap
The Lip Seal Flap is designed to help you get ideal seal between your lips and the STEALTH device for maximal airflow through device and maximal performance gains. If you cheat breathe through your nose or mouth, you will negate most of the benefits because breathing through nose or mouth not sealed is easy and will not elicit improved performance.
As stated in instructions for use, breath only through the device never your nose or unsealed mouth for maximal benefits and results improvement.
If you find yourself cheating through nose or mouth, lower your resistance level until you can use for entire workout.