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

from sys import stdin

input = stdin.readline
from itertools import groupby, accumulate


def solve():
    n = int(input())
    a = list(map(int, input().split()))
    # if len(set(a)) == 1:
    #     print(-1)
    #     return
    m = max(a)
    for i, v in enumerate(a):
        if v == m and (i > 0 and v > a[i-1] or i < n - 1 and v > a[i+1]):
            print(i+1)
            return
    print(-1)


if __name__ == '__main__':
    t = int(input())
    for _ in range(t):
        solve()
