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()))
    if len(a) == 1:
        print(1)
    elif len(a) == 2:
        if a[0] == a[1]:
            print(-1)
        else:
            if a[0] > a[1]:
                print(1)
            else:
                print(2)
    else:
        b = sorted(a)[::]
        if b[-1] == b[0]:
            print(-1)
        else:
            if a.count(b[-1]) == 1:
                print(a.index(b[-1]) + 1)
            else:
                if a[0] == b[-1] and a[1] < a[0]:
                    print(1)
                elif a[-1] == b[-1] and a[-2] < a[-1]:
                    print(n)
                else:
                    for i in range(1, n - 1):
                        if a[i] == b[-1] and (a[i] > a[i - 1] or a[i] > a[i + 1]):
                            print(i + 1)
                            break
