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

try:

    t = int(input())
    for _ in range(t):
        n = int(input())
        l = list(map(int, input().rstrip().split(' ')))[0:n]
        if len(set(l)) == 1:
            print(-1)
        else:
            MAX = max(l)
            for i in range(n):
                if l[i] == MAX and ((i < n-1 and l[i] > l[i+1]) or (i > 0 and l[i] > l[i-1])):
                    ind = i+1
                    break
            print(ind)


except:
    pass