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()))
    m = max(l)
    if l.count(m) == n:
        print(-1)

    else:
        f = 0
        for i in range(len(l)):
            if i == 0:
                if l[i] == m and l[i] > l[i+1]:
                    break

            if i == n-1:
                if l[i] == m and l[i] > l[i - 1]:
                        break

            if i != 0 and i != n-1:
                if l[i] == m and (l[i] > l[i - 1] or l[i] > l[i+1]):
                        break

        print(i+1)
        continue