Weather audio FadeOut audio when entering in caves

In our game we have a weather system.
The goal we want to obtain is:
Outside there is a thunderstorm and we enter in a cave; the deeper we go into the cave, the lower the volume of the weather (rain and thunders), and viceversa, of course when we return outside.

How can we obtains something that works well?
Trigger volumes and sound mix don’t help because the fade is fixed in blueprint/soundmix and we have no control on it: in fact, once a certain threshold is exceeded, the fade out starts, regardless of whether we are still or if we are going deep in the cave.