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 j in range(t):
    n = int(input())
    s = list(map(int, input().split()))
    ma = max(s)
    f = 0
    for i in range(n):
        if ma != s[i]:
            f = 1
            break
    if f == 0:
        print(-1)
    else:

        for i in range(n):
            if i == 0 and s[1] < s[0] and s[0] == ma:
                print(1)
                break
            elif i == n - 1 and s[n - 2] < s[n - 1] and s[n - 1] == ma:
                print(n)
                break
            elif i != 0 and i != n - 1:
                if (s[i] > s[i + 1] or s[i] > s[i - 1]) and s[i] == ma:
                    print(i + 1)
                    break


