If the altitude you're pinning the object to is determined by a raycast, that altitude value is going to be based on the current level of detail the map is being rendered at. When zooming out or in, the map data would change and so would the altitude of that specific LatLon.

If you don't need the 3D terrain, you could indeed render a flat map. See the Map Terrain Type for more info. This can be changed through the editor UI too.

If you'd like to continue using the 3D terrain, instead of pinning the object to the exact altitude value, use altiude = 0 and an AltitudeReferenceType of Surface for the MapPin. Then the shape's altitude would be updated to follow the terrain as it changes.