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

//package Codeforces;

import java.util.*;
import java.io.*;

public class C {
	static final int mod = (int) 1e9 + 7;
	static final int inf = (int) 1e9;
	static final long INF = (long) 1e18;

	public static void main(String[] args) throws IOException {
		FastScanner fs = new FastScanner();
		int T = fs.nextInt();
		while (T-- > 0) 
		{
			int n = fs.nextInt();
			int arr[] = new int[n];
			int index=0,max=-inf;
			Set<Integer> set = new HashSet<>();
			for(int i=0;i<n;i++)
			{
				arr[i]=fs.nextInt();
				int check=max;
				max=Math.max(max,arr[i]);
				if(max!=check)
					index=i;
				else if(arr[i]==max)
				{
					if((i!=n-1 && arr[i]>arr[i+1]) || (i!=0 && arr[i]>arr[i-1]))
						index=i;
				}
				set.add(arr[i]);
			}
			if(set.size()==1)System.out.println(-1);
			else System.out.println(index+1);
		}
	}
}
class FastScanner {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	StringTokenizer st = new StringTokenizer("");

	public String next() {
		while (!st.hasMoreTokens())
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException e) {
				e.printStackTrace();
			}
		return st.nextToken();

	}

	public String nextLine() throws IOException {
		return br.readLine();
	}

	int[] sort(int arr[]) {
		ArrayList<Integer> list = new ArrayList<Integer>();
		for (int i : arr)
			list.add(i);
		Collections.sort(list);
		for (int i = 0; i < arr.length; i++) {
			arr[i] = list.get(i);
		}
		return arr;
	}

	char[] charsort(char arr[]) {
		ArrayList<Character> list = new ArrayList<>();
		for (char c : arr)
			list.add(c);
		Collections.sort(list);
		for (int i = 0; i < list.size(); i++) {
			arr[i] = list.get(i);
		}
		return arr;
	}

	long[] longsort(long arr[]) {
		ArrayList<Long> list = new ArrayList<Long>();
		for (long i : arr)
			list.add(i);
		Collections.sort(list);
		for (int i = 0; i < arr.length; i++) {
			arr[i] = list.get(i);
		}
		return arr;
	}

	public int nextInt() {
		return Integer.parseInt(next());
	}

	public int[] readArray(int n) {
		int[] arr = new int[n];
		for (int i = 0; i < n; i++)
			arr[i] = nextInt();
		return arr;
	}

	public long nextLong() {
		return Long.parseLong(next());
	}

	public long[] longreadArray(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nextLong();
		return a;
	}
}
