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 sys
t=int(input())
for i in range(t):
    n=int(input())
    lst=list(map(int,input().split()))
    def solve_second():    
       m=max(lst)
       for i in range(n):
            if(lst[i]==m):
                if(i-1>=0 and lst[i-1]<lst[i]):
                    print(i+1)
                    return
        
                if(i+1<n and lst[i+1]<lst[i]):
                    print(i+1)
                    return
    def solve():
        flag=1
        for i in range(n):
            if(lst[i]!=lst[0]):
                flag=0
                break;
        if(flag):
            print('-1')
            return
        else:
            solve_second()
    solve()
            
            