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

for _ in range(int(input())):
    n = int(input())
    a = list(map(int, input().split()))

    if a.count(max(a)) == 1:
        print(a.index(max(a)) + 1)
        continue

    ml = [0] * n
    mr = [0] * n

    for i in range(1, n):
        if a[i-1] < a[i]:
            ml[i] = ml[i-1] + 1

    for i in range(n-2, -1, -1):
        if a[i+1] < a[i]:
            mr[i] = mr[i+1] + 1

    m = [ml[i] + mr[i] for i in range(n)]

    if max(m) == min(m):
        print(-1)
    else:
        print(m.index(max(m)) + 1)
