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

def solve():
    n = int(input())
    a = list(map(int, input().split()))
    m, ans = max(a), 0

    for i in range(n):
        if i == 0 and a[i] == m:
            if ((i + 1) < n) and (a[i + 1] < a[i]):
                ans = i + 1
                break
        elif i == n - 1 and a[i] == m and a[i] > a[i - 1]:
            ans = i + 1
            break

        elif i != 0 and i != n- 1 and a[i] == m and ((a[i - 1] < a[i]) or (a[i + 1] < a[i])):
                ans = i + 1
                break

    print(ans if ans != 0 else -1)


for _ in range(int(input())):
    solve()