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.util.Scanner;

/**
 *
 * @author meimarcel
 */
public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int t = input.nextInt();
        while(t > 0) {
            int n = input.nextInt();
            int seq[] = new int[n];
            int maior = -1;
            boolean igual = true;
            for(int i = 0; i < n; ++i) {
                int k = input.nextInt();
                seq[i] = k;
                if(k > maior) {
                    maior = k;
                }
                if(i != 0 && k != seq[i-1] && igual) {
                    igual = false;
                }
            }
            
            if(igual) {
                System.out.println(-1);
            } else {
                boolean can = false;
                int index = -1;
                for(int i = 0; i < n; ++i) {
                    if(seq[i] == maior) {
                        if(i != 0) {
                            if(seq[i-1] < seq[i]) {
                                index = i+1;
                                can = true;
                                break;
                            }
                        }
                        if(i != n-1) {
                            if(seq[i+1] < seq[i]) {
                                index = i+1;
                                can = true;
                                break;
                            }
                        }
                    }
                }
                if(can) {
                    System.out.println(index);
                } else {
                    System.out.println(-1);
                }
            }
            
            t--;
        }
    }
    
}
