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

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

    max = 0
    max_mas = []
    for i in range(n):
        if a[i] > max:
            max = a[i]
            max_mas = [i]
        elif a[i] == max:
            max_mas += [i]

    if max_mas == list(range(len(a))):
        print(-1)
    else:
        for i in max_mas:
            if (i-1>=0 and a[i-1] < a[i]) or (i+1<=n and a[i+1] < a[i]):
                print(i+1)
                break