How can you know if you are mouth breathing?

I've always used a nasal mask for CPAP therapy. My mouth and throat would be dry if the water level in my "dinosaur" passover humidifier got low. Now I have a new S9 with H5i Humidifier and ClimateLine. The setting is "auto" for Climate Control. I wake in the morning with very dry mouth but throat and nose are just fine.

How can I know if the problem is mouth breathing? I'm currently using an S9 ESCAPE while I wait for my S9 ELITE to arrive in a few days. Will the S9 ELITE show a "leak" if I'm mouth breathing? Can it tell the difference between a mask leak and mouth breathing? I'm tempted to get a chin strap to see if it changes anything. I really don't want to use a FF mask. The leaks are so bad on those. Any ideas?