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;

public class C{

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int t = sc.nextInt();
        sc.nextLine();
        while (t-- > 0){
            int n = sc.nextInt();
            sc.nextLine();
            int[] arr = new int[n];
            boolean allEqual = true;
            int max = 0;
            for(int i = 0; i < n; i++){
                arr[i] = sc.nextInt();
            }
            int ans = -1;
            for(int i = 0; i < n; i++){
 
                if (i > 0 && arr[i] != arr[i-1]){
                    allEqual = false;
                   

                }

                 if (arr[i] >= arr[max]){
                        max = i;
                        if (i - 1 >= 0 && arr[i] > arr[i-1]){
                            ans = i;
                        }
                        if (i + 1 < n && arr[i] > arr[i+1]){
                            ans = i;
                        }
                    }
            }

            if (allEqual) {
                System.out.println("-1");
                continue;
            }

            System.out.println(ans+1);

        }
    }
}