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


from collections import deque
def solve(arr , n ):

    mx = max(arr)
    ans = -1

    for i in range(n - 1):
        if arr[i] == mx and l[i+1] < mx:
            ans = i + 1

        elif arr[i+1] == mx and arr[i] < mx :
            ans = i + 2

    return ans



for tt in range(int(input())):
    n = int(input())
    l = list(map(int,input().split()))

    res = solve(l  , n)
    d =deque()
    d.append(res)

    for i in d :
        print(i)



