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 n == 2:
        if l[0] == l[1]:
            print(-1)
        else:
            print(l.index(max(l))+1)
    else:
        valid_ps = []

        if l[-2] < l[-1]:
            valid_ps.append(n-1)

        if l[0] > l[1]:
            valid_ps.append(0)

        for i in range(1, n-1):
            if (l[i-1] < l[i] and l[i+1] <= l[i]) or (l[i+1] < l[i] and l[i-1] <= l[i]):
                valid_ps.append(i)

        if len(valid_ps) == 0:
            print(-1)
            continue

        print(max(valid_ps, key=lambda x: l[x])+1)
