The oral cavity and the tongue can be different for each person. Therefore, you may have to adjust your gag for your needs. For the tongue frenulum there is a prepared place to cut out. If the vacuum effect is too strong, you can reduce it by cutting a hole in the front of the tongue area. 

Cut out for tongue frenulum with scissors.

  

 

Cut out for tongue frenulum with revolver punch pliers and scissors

Remove vacuum effect by punching hole