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

T=int(input())
def f(l,n):
    m=max(l)
    s=-1
    ll=list(set(l))
    if(len(ll)==1):
        return -1
    for i in range(n):
        if(l[i]==m):
            if(i>0 and l[i-1]<m):
                return i+1
            elif(i<n-1 and l[i+1]<m):
                return i+1
                
            
    return s
            
    
while(T):
    n=int(input())
    l=[int(k) for k in input().split()]
    print(f(l,n))
    
    
    T-=1