Cave mesh inside mountain holes - how to align?

I’m trying to create a cave on my level. I got a mountain using a landscape, and I want to create a cave on one of the mountain “walls”. I created a hole using the invisibility tool in the landscape tool, and put the cave in there. But how can I align the landscape to encapsulate the cave exactly?

if it’s too much - it will get inside the cave. If it’s not enough - there will be holes between the caves and the mountain.

Attaching 2 pictures showing th

e different states (too big hole, too small hole)