Most people cannot really spot if an object (like a building, ship or asteroid) is at the right height for a collision, because most screens are still displaying in 2D.
Please add a colored glowing outline to those parts of an object that are at collision height.
For example, if part of a huge spherical ateroid would be at collision height, there would be a red glowing circle surrounding it, indicating where the ship could touch it.
Alternatively you could add a semi-transparen layer (or grid) at the ships height. People could spot the collision height of objects, by distinguishing between whats below the layer and whats above it.