My characters in Unity float slightly above my ground I imported and made in Blender

I've created a very simple plane, no ups and downs. A simple plane. All the characters, with proper gravity settings, worked just fine. The moment I add a hill/ramp/structure, the characters will float above the bottom plane, and you are free to move around. The engine thinks you are on the ground but you are not. You can jump off of this "non-ground" and go to the higher point of my terrain build. At the highest point in any of my terrain builds, gravity is normalized, but only in that area. And there are no seemingly invisible layers of "compressed air" or "invisible floor" on planes built in Unity. I want to inqiure why this happens only with my Blender made terrains. I export them and import them into Unity as an FBX file. And my process so far was to construct and sculpt terrain, and then send it to Unity. But like I said, whenever I add any height or depth to a terrain, there's a problem where the character will float on the lower plane or terrain. I really need help I have no idea what it could be. We checked the mesh collider and the player is well above the collider. Please help, it's stopping from any progress being made.