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

#code

R = lambda:map(int,input().split())


for _ in range(int(input())):
    n = int(input())
    arr = list(R())
    if len(set(arr)) == 1:
        print(-1)
    else:
        max_val = max(arr)
        for i in range(n):
            f = 0
            if i and arr[i-1] < arr[i]:
                f = 1
            if i+1 < n and arr[i+1] < arr[i]:
                f = 1
            if f and arr[i] == max_val:
                print(i+1)
                break