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

# cook your dish here
t = int(input())
for _ in range(t):
    n = int(input())
    li = list(map(int, input().split()))
    max_ele = max(li)
    if li == [max_ele] * n:
        print("-1")
        continue
    for ind, i in enumerate(li):
        if i == max_ele:
            li[ind] = 1 
        else:
            li[ind] = 0 
    for ind, i in enumerate(li):
        if ind + 1 < n:
            if i == 1 and li[ind + 1]  == 0:
                print(ind + 1)
                break
            if i == 0 and li[ind + 1] == 1:
                print(ind + 1 + 1)
                break 
    