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

for _ in range(int(input())):
    n = int(input())
    l = list(map(int, input().split()))
    if len(set(l)) == 1:
        print(-1)
    else:
        l.append(-1)
        ans = n
        if l[0] > l[1]:
            ans = 0
        if l[n - 1] > l[n - 2] and l[n - 1] > l[ans]:
            ans = n - 1
        for i in range(1, n - 1):
            if l[i] > l[ans]:
                if l[i] > l[i + 1] or l[i] > l[i - 1]:
                    ans = i
        print(ans + 1)
