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) {
		// TODO Auto-generated method stub
		Scanner s = new Scanner(System.in);
		int t = s.nextInt();
		while(t-->0) {
			int n = s.nextInt();
			int[] arr = new int[n];
			for(int i=0;i<n;i++) arr[i] = s.nextInt();
			boolean distinct = false;
			int lastNum = arr[0];
			int max = arr[0];
			for(int i=1;i<n;i++) {
				if(arr[i]!=lastNum) distinct = true;
				max = Math.max(max, arr[i]);
				lastNum = arr[i];
			}
			if(!distinct) {
				System.out.println(-1);
				continue;
			}
			
			for(int i=0;i<n;i++) {
				if(arr[i]==max) {
					if(i-1>=0 && arr[i-1]!=max) {
						System.out.println(i+1);
						break;
					} else if(i+1<n && arr[i+1]!=max) {
						System.out.println(i+1);
						break;
					}
				}
			}
			
		}
	}

}
