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.*;
import java.util.*;

public class Main {
	public static void main(String[] args) throws FileNotFoundException,IOException {
        boolean isFile = true;
        isFile &= false;
        ScanReader in;PrintWriter out;

        if(isFile) {
            InputStream inputStream = new FileInputStream("input.txt");
            in = new ScanReader(inputStream,new BufferedReader(new FileReader("input.txt")));
            out = new PrintWriter(new BufferedWriter(new FileWriter("output.txt")));

        } else {
            InputStream inputStream = System.in;
            in = new ScanReader(inputStream,new BufferedReader(new InputStreamReader(System.in)));
            out = new PrintWriter(System.out);
        }

        Palindrome solver = new Palindrome();

        int t = 1;
        t = in.nextInt();

        for (int i = 0; i < t; i++) {
            solver.solve(i + 1, in, out);
        }

        out.close();
	}

    static class Palindrome {
        static long mod = 1000000007;
        static long maxX = (long) 1e18;
        static long mod2 = 998244353;

        //  Check for boundary Condition because you are not Sehwag..
        //  For multiple Test cases take all input -> do not use return while taking input.
        //  at least check constraint for once it can be done in nested loops.
        //  Think simple and short
        //  check for proof of solution
        //  Read editorial after contest.....
        

        void solve(int testNumber, ScanReader in, PrintWriter out) {
        	int n = in.nextInt();
        	int[] a = new int[n];
        	int max  = -1;
        	for(int i = 0;i<n;i++) {
        		a[i] = in.nextInt();
        		max = Math.max(max,a[i]);
        	}

        	for(int i =0;i<n;i++ ) {
        		if(a[i] == max && (( i> 0 && a[i-1] < a[i]) || (i+1 < n && a[i+1] < a[i]))) {
        			out.println(i+1);
        			return;
        		}
        	}

        	out.println(-1);
        }
    }
    
    static class ScanReader {
        private final InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;
        private BufferedReader br;

        public ScanReader(InputStream stream,BufferedReader br) {
        this.stream = stream;
            this.br = br;
        }

        public int read() {
            if (numChars == -1)
                throw new InputMismatchException();

            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }

                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

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

        public int nextInt() {
            int c = read(); 

            while (isSpaceChar(c))
                c = read();

            int sgn = 1;

            if (c == '-') {
                sgn = -1;
                c = read();
            }

            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));

            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;

            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
            return res * sgn;
        }

        public double nextDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }

        public String readString() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            }
            while (!isSpaceChar(c));

            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public String next() {
            return readString();
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }}
}