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 func(n, arr):
    s = set(arr)
    if len(s) == 1:
        print(-1)
        return
    maxm = max(arr)
    if arr[0] == maxm:
        if arr[1] < maxm:
            print(1)
            return
    for i in range(1, n-1):
        if arr[i] == maxm:
            temp = arr[i]
            if temp > arr[i-1]:
                print(i+1)
                return
            if temp > arr[i+1]:
                print(i+1)
                return
    if arr[-1] == maxm:
        print(n)
t = int(input())
for _ in range(t):
    n = int(input())
    arr = list(map(int, input().split()))
    func(n, arr)