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.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Main {
    static final MyScanner in = new MyScanner();
    static final MyWriter myOut = new MyWriter();
    static final PrintWriter out = myOut.out;

    public static void main(String[] args) {
        int n = in.nextInt();
        while (n-- > 0) {
            boolean fg = true;
            int m = in.nextInt();
            int[] arr = new int[m];
            in.readInArray(arr);
            int max = Integer.MIN_VALUE;
            int idx = -1;
            for (int i = 0; i < m; i++) {
                if (max < arr[i]) {
                    max = arr[i];
                    idx = i;
                }
            }
            int[] temp = new int[m + 2];
            temp[0] = Integer.MAX_VALUE;
            temp[m + 1] = Integer.MAX_VALUE;
            for (int i = 1; i <= m; i++) {
                temp[i] = arr[i - 1];
            }
            for (int i = 1; i < m + 2; i++) {
                if (temp[i] == max && (temp[i] > temp[i - 1] || temp[i] > temp[i + 1])) {
                    out.println(i);
                    fg = false;
                    break;
                }
            }
            if (fg) {
                out.println(-1);
            }
//            int start = arr[0];
//            int sum = arr[0];
//            int left = 0;
//            for (int i = 1; i < m; i++) {
//                if (arr[i] < sum) {
//                    sum++;
//                } else if (arr[i] == sum) {
//                    continue;
//                } else {
//                    left = i;
//                    sum = i - left + arr[i];
//                }
//            }
//            if (sum == arr[0]) {
//                out.println(-1);
//            } else if (left == 0) {
//                while (left < m - 1 && arr[left] == arr[left + 1]) {
//                    left++;
//                }
//                out.println(left + 1);
//            } else
//                out.println(left + 1);
        }
        out.flush();
        out.close();

    }

    private static class MyWriter {

        private PrintWriter out;

        public MyWriter() {
            out = new PrintWriter(System.out);
        }

        void printlnArray(int[] arr, int start, int end) {
            for (int i = start; i < end; i++) {
                out.println(arr[i]);
            }
        }

        void printArrayJoinSpace(int[] arr, int start, int end) {
            for (int i = start; i < end; i++) {
                out.println(arr[i] + " ");
            }
        }

        void printlnArray(int[] arr) {
            for (int x : arr) {
                System.out.println(x);
            }
        }

        void printArrayJoinSpace(int[] arr) {
            for (int i : arr) {
                System.out.print(i + " ");
            }
        }

    }

    private static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

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

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

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

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }


        public static int leastInterval(char[] tasks, int n) {
            int i = 0;
            do {
                System.out.println(1);
            } while (i++ < 10);

            String[] split = "0.1".split("\\.");
            System.out.println(Arrays.toString(split));
            return 0;
        }

        public void readInArray(int[] arr, int start, int end) {
            for (int i = start; i < end; i++) {
                arr[i] = nextInt();
            }
        }

        public void readInArray(int[] arr) {
            for (int i = 0; i < arr.length; i++) {
                arr[i] = nextInt();
            }
        }
    }


}


