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.*;

public class DominantPiranha {
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        int cases = Integer.parseInt(in.readLine());
        for (int i = 0; i < cases; i++) {
            in.readLine();
            String[] curAq = in.readLine().split(" ");
            int max = Integer.parseInt(curAq[0]);
            int candIndex = -2;
            for (int j = 1; j < curAq.length; j++) {
                int curInt = Integer.parseInt(curAq[j]);
                if (curInt > max) {
                    max = curInt;
                    candIndex = j;
                } else if (curInt < max) {
                    if (Integer.parseInt(curAq[j - 1]) > curInt) {
                        candIndex = j - 1;
                    }
                }
            }
            out.println(candIndex + 1);
        }
        out.close();
        in.close();
    }
}
