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

import sys
input = sys.stdin.readline


def solve():
    t = int(input())
    for _ in range(t):
        n = int(input())
        a = list(map(int, input().split()))
        max_a = max(a)

        if n == 1:
            print(1)
            continue

        maybe_dominant = []
        for i in range(n):
            if i - 1 >= 0 and a[i] > a[i-1]:
                maybe_dominant.append(i)
                continue
            if i + 1 < n and a[i] > a[i + 1]:
                maybe_dominant.append(i)

        if not maybe_dominant:
            print(-1)
            continue

        for index in maybe_dominant:
            if a[index] == max_a:
                print(index + 1)
                break


solve()
