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.util.Scanner; 
import java.util.StringTokenizer; 
import java.util.*;
  
public class c677c
{ 
    //By shwetank_verma
    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 (IOException e) 
            { 
                e.printStackTrace(); 
            } 
            return str; 
        } 
    } 
    static int mod=1000000007;
    static boolean primes[]=new boolean[1000007];
    
    static boolean seive(int n){
        Arrays.fill(primes,true);
        primes[0]=primes[1]=false;
        for(int i=2;i*i<=n;i++){
            if(primes[i]==true){
                for(int p=i*i;p<=n;p+=i){
                    primes[p]=false;
                }
            }
        }
        if(n<1000007){
            return primes[n];
        }
        return false;
        
    }
    static int gcd(int a,int b){
        if(b==0)
        return a;
        return gcd(b,a%b);
    }
    static long GCD(long a,long b){
        if(b==0)
        return a;
        return GCD(b,a%b);
    }
    
  
    public static void main(String[] args) 
    { 
        FastReader sc=new FastReader(); 
        try{
           
                int t=sc.nextInt();
                while(t-->0){
                int n=sc.nextInt();
                
                int a[]=new int[n];
                int max=Integer.MIN_VALUE;
                for(int i=0;i<n;i++){
                    a[i]=sc.nextInt();
                    if(a[i]>max)
                    	max=a[i];
                    
                }
                
                int ans1=-1,v1=0;
                int ans2=-1,v2=0;
                for(int i=1;i<n;i++) {
                	if(a[i]>a[i-1]&&a[i]==max)
                	{
                		ans1=i;
                	}
                		
                }
                for(int i=0;i<n-1;i++) {
                	if(a[i]>a[i+1]&&a[i]==max)
                		ans2=i;
                }
                if(ans1==-1&&ans2==-1)
                	System.out.println(-1);
                else if(ans1==-1)
                	System.out.println(ans2+1);
                else if(ans2==-1)
                	System.out.println(ans1+1);
                else
                	System.out.println(ans1+1);
        
                }
           
            
        }catch(Exception e){
            return;
        }
    } 
}
