Raise/Lower Landscape's Default Grid Position?

I believe I made the mistake of building my landscape backwards. As you can see in the image, the landscape grid is placed at the base of the building to the right. From the building, the terrain begins to slope downward. Seems okay, but in hindsight, I think I should’ve built the terrain upwards towards the building.

This is a problem because when the player character walks too far beneath the landscape grid, the game freezes because the player exceeds the level bounds.

I don’t believe it’s possible to lower the landscape grid, but I really don’t want to rebuild my entire landscape because of my oversight. The only other alternative I can think of would be to raise each individual level actor on the Z axis, one by one, by a specific distance until everything is aligned with the terrain again.

But before I try that, I’m wondering if there’s a way to save a lot of time and just lower the default landscape grid location.