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

# -*- coding: utf-8 -*-
"""
Created on Wed Oct 21 21:19:34 2020

@author: Admin
"""
for k in range(int(input())):
    h=input()
    l=[int(i) for i in input().split()]
    z=max(l)
    f=0
    if len(set(l))==1:
        print(-1)
    else:
        if l.count(z)==1:
            print(l.index(z)+1)
        else:
            for i in range(len(l)):
                if f==1:
                    break
                if i==0:
                    if l[i]==z:
                        if l[i+1]<z:
                            f=1
                            print(i+1)
                            
                            continue
                if i==len(l)-1:
                    if l[i]==z:
                        if l[i-1]<z:
                            f=1
                            print(i+1)
                            continue
                if 0<i<len(l)-1:
                    if l[i]==z:
                        if l[i+1]<z or l[i-1]<z:
                            f=1
                            print(i+1)
                            continue
                        
                        