The format of the terrain in Event Horizon should be roughly similar from table to table.
If you believe the terrain has been materially altered, contact a judge!
For reference, each table should have one terrain piece near the centre of the board, one in each table quarter, and possibly some additional small pieces scattered about.
For Event Horizon, terrains are placed as follows:
The table should have roughly 7 pieces of terrain, covering approximately 25% of the table, with most or all of it having some area component
At least three pieces of terrain should have significant line of sight blocking components, with some even capable of blocking full line of sight to a vehicle or monstrous creature similar to a carnifex, rhino, or even land raider and leman russ.
One larger pieces of line of sight blocking area terrain should be roughly placed at the centre of the table. One other large pieces of area terrain should be placed in each table quarter. A couple of smaller pieces might be used in the larger gaps of open space on the table. Placement would be roughly equal regardless of deployment type or side chosen.
Practicing with terrain roughly set in this fashion will help you prepare for Event Horizon. While we will have a very wide variety of terrain pieces from table to table, the placement of the terrain will be roughly similar on all tables.