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())
for i in range(t):
    n = int(input())
    a = [int(x) for x in input().split()]
    m = max(a)
    mc = a.count(m)
    if mc == n:
        print(-1)
    elif mc == 1:
        print(a.index(m)+1)
    else:
        ans = 0
        for i in range(n):
            if a[i] == m and i+1!=n and a[i+1]<m:
                ans = i+1
                break
            elif a[i] == m and i!=0 and a[i-1]<m:
                ans = i+1
            else:
                pass
        print(ans)
                
            
        
                
            
        
    