Rays do not detect terrain and prefabs do not spawn where wanted

Hello, i have created script which instantiates prefab on maps on all possible spawnpoints. It searches for all spawnpoints and puts them on List. Then, it calls a function which casts a ray downwards from position of spawnpoint in search for suitable terrain to spawn tree. There are few things that may fail, but i always want it to spawn few trees on one spawnpoint, 3 for example. This will enforce it to cast 3 times, but it might fail and not hit terrain. But it does hit 99% times, so it is not a big problem if some spawnpoints creates only 2 trees. The problem is, that even if 99% of the rays hit the ground, most of them do not make contact. I used Debug.Line to demonstrate this:

The things on mountain are trees which are supposed to spawn on the point of contact with terrain. My code (code might miss a brace or two because i needed to trim out long commented areas and i might have trimmed too much):

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class raySpawn : MonoBehaviour {
 //public GameObject[] propy = new GameObject[30];
 public GameObject [] brzozy = new GameObject [5];
 public GameObject[] kamole = new GameObject[10];
 private Vector3 origin;
 private int index = 0;
 private bool czyIndexPoprawny = false;
 public GameObject parent;
 private int odl = 0;
 public int iloscPropow = 90;
 public int iloscSkał = 2000;
 private int zrespionePropy = 0;
     // Use this for initialization
     void Start () {
         SkierujZwierzeta(); //DOESNT MATTER
         origin = gameObject.transform.position;
         RaycastHit hit;
         List<GameObject> spawnOzdob = new List<GameObject>();
         GameObject[] spawnOzdobTable;
         spawnOzdobTable = GameObject.FindGameObjectsWithTag("SpawnOzdoby");
         spawnOzdob.AddRange(spawnOzdobTable);
         //PROPY
         for(int i = 0; i < spawnOzdob.Count; i++)
         {
             Vector3 origin = new Vector3(spawnOzdob[i].transform.position.x,spawnOzdob[i].transform.position.y+5,spawnOzdob[i].transform.position.z);
             switch(spawnOzdob[i].name)
             {
                 default:
                     Debug.Log("Nie wykryto żadnych spawnów pod akceptowanymi nazwami");
                     break;
                 case "SpawnBrzozy":
                     SpawnujWColliderze(origin, brzozy, Random.Range(0,5),10);
                     break;
             }
         }
     }
         
     void FixedUpdate(){ //DOES NOT MATTER IN THIS CASE
         odl++;
         if(odl == 3000)
         {
             odl = 0;
             SkierujZwierzeta();
         }
     }
     void SpawnujWColliderze(Vector3 origin, GameObject[] zbiór, int index, int gęstość)
     {
         Debug.Log("Przygotowuje sie do spawnowania spawnOzdob");
         RaycastHit hit;
         for(int i = 0; i < gęstość;i++)
         {
             Vector3 cel = new Vector3(origin.x+Random.Range(-16,16),origin.y-10,origin.z+Random.Range(-16,16));
             Debug.DrawLine(origin,cel,Color.red,1000);
             Ray linia = new Ray(origin, cel);
             if(Physics.Raycast(linia, out hit))
             {
                 Debug.Log("Raycast wystrzelony");
                 if(hit.transform.tag == "ZaczepBudowy")
                 {
                     Debug.DrawLine(origin,cel,Color.green,1000);
                     //i++;
                     Debug.Log("Zespawnowałem ozdobę");
                     //zrespionePropy++;
                     GameObject obiekt = Instantiate(zbiór[index],hit.point,Quaternion.identity) as GameObject;
                     obiekt.AddComponent<UnityEngine.AI.NavMeshObstacle>().carving = true;
                     obiekt.transform.parent = parent.transform;
                 }
                 else if(hit.transform.tag != "ZaczepBudowy")
                 {
                     //i--;
                 }
             }
         }
     }
     void SkierujZwierzeta(){ //COMPLETELY DOESNT MATTER IN THIS PROBLEM
         Debug.Log("Przesylam pozycje ruchu");
             RaycastHit hit;
             Ray linia = new Ray(gameObject.transform.position, new Vector3(Random.Range(-1000,1000), -500, Random.Range(-1000,1000)));
             if(Physics.Raycast(linia,out hit) && hit.transform.tag == "ZaczepBudowy")
             {
                 if(hit.point.y > 24)
                 {
                     GameObject.FindGameObjectWithTag("Zwierze").SendMessage("ZmienCel",hit.point,SendMessageOptions.DontRequireReceiver);
                 }
             }
             else
                 SkierujZwierzeta();
     }
 }

I assume that the problem is related to how my code handles rays, but i dont know. Can someone help me?