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.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Test {
	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		PrintWriter pw = new PrintWriter(System.out);
		int t = sc.nextInt();
		while (t-- > 0) {
			int n = sc.nextInt();
			int[] a = new int[n];
			for (int i = 0; i < n; i++)
				a[i] = sc.nextInt();
			int max = a[0];
			int maxi = 1;
			boolean change = false;
			for (int i = 2; i <= n; i++) {
				int x = a[i - 1];
				if (x != max)
					change = true;
				if (x >= max) {
					if(a[i-2]== x) {
						if(!(i == n || (i!=n && a[i] == x)) ){
							maxi = i;
							max = x;
						}
					}else {
						maxi = i;
						max = x;
					}
				}
			}
			if (change)
				pw.println(maxi);
			else
				pw.println(-1);
		}

		pw.close();
	}

	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

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

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

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

		public double nextDouble() throws IOException {
			String x = next();
			StringBuilder sb = new StringBuilder("0");
			double res = 0, f = 1;
			boolean dec = false, neg = false;
			int start = 0;
			if (x.charAt(0) == '-') {
				neg = true;
				start++;
			}
			for (int i = start; i < x.length(); i++)
				if (x.charAt(i) == '.') {
					res = Long.parseLong(sb.toString());
					sb = new StringBuilder("0");
					dec = true;
				} else {
					sb.append(x.charAt(i));
					if (dec)
						f *= 10;
				}
			res += Long.parseLong(sb.toString()) / f;
			return res * (neg ? -1 : 1);
		}

		public int[] nextIntArray(int n) throws NumberFormatException, IOException {
			int[] t = new int[n];
			for (int i = 0; i < n; i++) {
				t[n] = Integer.parseInt(next());
			}
			return t;
		}

		public boolean ready() throws IOException {
			return br.ready();
		}

	}
}
