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 = list(map(int,input().split()))
    m = 0
    k = 0
    d = 0
    for j in range(n):
        if A[j] > m:
            k = 1
            m = A[j]
            if j > 0 and A[j - 1] != m or j < n - 1 and A[j + 1] != m:
                d = j + 1
        elif A[j] == m:
            k += 1
            if j > 0 and A[j - 1] != m or j < n - 1 and A[j + 1] != m:
                d = j + 1
    if n == k:
        print(-1)
    else:
        print(d)