Caves for Unreal Engine - convenient workflow

I’m doing a caves for my terrain. I have 2 solution, but none are good enough
Caves are just a simple shapes - later I’m going to improve

The problem is - to merge a landscape and a caves
Solution I know are
• using UE’s Landscape System
• and without

Single-mesh terrain

Caves - via mesh boolean
Caves-1-frames025--KGy-SOFT-16g-320
+clean merge line
+simple workflow
-is not compatible with UE Landscape System

UE Landscape using Visibility Mask

It also affects collision (is enterable hole)
Caves are sepatate mesh
Caves-2--f025-BW-360
Caves-3--f025-BW-360
+UE Landscape System
-merge line are awful

Overall, Lanscape System gives to much out of a box, so I can simply drop it, and switch to a simple mesh

:-1:Seems only way for now - to fill a gaps with other meshes
:-1:Blend a landscape with a mesh - is also not a case. It just a visual blend. Mesh accurately placed on atop of Landscape

So, let me know, if you have a solution/idea - how to nicely merge a Landscape with a cave mesh