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.*;
import java.math.*;

public class C {
    public static void main(String[] args) throws IOException {
        FastScanner fs=new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        // int T = 1;

        int T=fs.nextInt();
        for (int tt=0; tt<T; tt++) {
            int n = fs.nextInt();
            int[] arr = fs.readArray(n);
            int ans = -1;
            int max = -1;
            for (int i=0; i<n; i++) {
                max = Math.max(max, arr[i]);
            }
            for (int i=1; i<n; i++) {
                if (arr[i-1]==max && arr[i]!=max) {
                    ans = i;
                    break;
                }
            }
            if (ans==-1 && arr[n-1]==max && arr[n-2]!=max) {
                ans=n;
            }
            out.println(ans);
        }
        
        out.close();
    }

    static final Random random=new Random();
    
    static void ruffleSort(int[] a) {
        int n=a.length;//shuffle, then sort 
        for (int i=0; i<n; i++) {
            int oi=random.nextInt(n), temp=a[oi];
            a[oi]=a[i]; a[i]=temp;
        }
        Arrays.sort(a);
    }
    
    static class FastScanner {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st=new StringTokenizer("");
        String next() {
            while (!st.hasMoreTokens())
                try {
                    st=new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            return st.nextToken();
        }
        
        int nextInt() {
            return Integer.parseInt(next());
        }
        int[] readArray(int n) {
            int[] a=new int[n];
            for (int i=0; i<n; i++) a[i]=nextInt();
            return a;
        }
        long nextLong() {
            return Long.parseLong(next());
        }
    }

}
