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.util.*;
import java.lang.*;
import java.io.*;
import java.math.BigInteger;

public class Main
{
    static class FastReader{
        BufferedReader br;
        StringTokenizer st;
        public FastReader(){
            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 (Exception e){
                e.printStackTrace();
            }
            return str;
        }
        int[] readArray(int n){
            int[] a = new int[n];
            for(int i = 0; i < n; i++){
                a[i] = nextInt();
            }
            return a;
        }
    }
    static int modPower(int x, int y, int mod){
        int res = 1;
        x %= mod;
        if(x==0) return 0;
        while(y>0){
            if(y%2==1){
                res = (res*x)%mod;
            }
            y = y>>1;
            x = (x*x)%mod;
        }
        return res;
    }
    static class pair<T1, T2>{
        T1 first;
        T2 second;
        pair(T1 first, T2 second){
            this.first = first;
            this.second = second;
        }
    }
    static int gcd(int a, int b){
        if(b == 0) return a;
        return gcd(b, a%b);
    }

    public static void main (String[] args) throws java.lang.Exception
    {
        FastReader in = new FastReader();
        int t = in.nextInt();
        while(t-->0){
            int n = in.nextInt();
            int[] a = new int[n];
            Set<Integer> s = new HashSet<>();
            int mx = 0;
            for(int i = 0; i < n; i++){
                a[i] = in.nextInt();
                s.add(a[i]);
                mx = Math.max(mx, a[i]);
            }
            if(s.size() == 1){
                System.out.println("-1");
            } else {
                int ans = -1;
                for(int i = 0; i < n; i++){
                    if(a[i] == mx){
                        if((i > 0 && a[i-1] != mx) || (i < (n-1) && a[i+1] != mx)){
                            ans = i+1; break;
                        }
                    }
                }
                System.out.println(ans);
            }
        }
    }
}
