1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

import java.io.*;
import java.util.*;
/**
 *
 * @author Aaryan
 * AV 
 */
public class Test {
    public static void main(String[] args) throws Exception {
       BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        String str11 [] = br.readLine().split(" ");
       int tc = Integer.parseInt(str11[0]);
        
        while(tc-->0){
             String str12 [] = br.readLine().split(" ");
       int n = Integer.parseInt(str12[0]);
      String str [] = br.readLine().split(" ");
            int a [] = new int[n];
           int same=0;int ind=0;
            for(int i=0; i<a.length; i++){
                a[i]=Integer.parseInt(str[i]);
             }
             int max = Arrays.stream(a).max().getAsInt();
            for(int i=0; i<a.length; i++){
                if(a[i]==max){
                    same++;
                    
                }
            }
            for(int i=0; i<a.length; i++){
                if(i!=(n-1)){
                    
                
                if(a[i]==max){
                    if(a[i]>a[i+1]){
                        ind=i+1;
                        break;
                    }
                }
                }
                if(i!=0){
                if(a[i]==max){
                    if(a[i]>a[i-1]){
                        ind=i+1;
                        break;
                    }
                }
                }
                
               
            }
            
            
           
           if(same<n){
                out.println(ind);
           
            out.flush(); 
           }
           else{
               out.println("-1");
           
            out.flush(); 
               
           }
            
            
            
           
        }
        
        
    }
}