Since the release of 9th Edition Warhammer 40k, the terrain has seen a major overhaul in how it is used on the battlefield. Smaller games are requiring smaller terrain pieces especially when you are using obscuring rules, and I'm personally using the smaller pieces to create more dynamic fields of fire within my games.

But what about massive terrain pieces? can they still be used on the smaller table without the problem of simply moving a short distance onto the area terrain piece and being able to see right through the terrain with it having little effect.
One way to combat the problem of the terrain piece losing Obscuring is to place large LOS blocking pieces of terrain inside the area, but that came with its own pitfalls, and what if you don't have additional terrain? not everybody has the money to access everything.

To find a simple solution I delved into my mind palace and retrieved some accent old STC tech on using Area terrain in games. My mind travelled back to the 4th edition of the game (still one of the best editions in my opinion) and the rules for area terrain here, could easily apply to the modern game with a little modification.
So here I present the rules (with examples) on how to use large-scale area terrain in your games of Warhammer 40k.
Large scale area terrain pieces replace the obscuring keyword with the Large Scale Obscuring keyword. All other rules for the terrain type remain the same.
The following rules apply to Large Scale Obscuring terrain pieces.
Blocks visibility while trying to fire through the Area Terrain. (Unless targetting an AIRCRAFT or a unit with 18+ wounds.
INFANTRY, BEASTS, VEHICLE and SWARM units inside the terrain feature footprint can only be seen if they are within 6inch of the terrains footprint edge, also they can only shoot out of the terrain if they are within 6inch of the edge. (This doesn't apply to Titanic Units)

Enemy Units within the Area terrain can see each using the true line of sight rules.
VEHICLE, TITANIC, MONSTER and AIRCRAFT units will receive the benefits of Light Cover if at least one part of the terrain feature is at least 8inch tall.