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

def domi_pira(arr):
    if len(set(arr))==1:
        return -1
    m = max(arr)
    if arr[0]==m and arr[1]<arr[0]:
        return 1
    elif arr[-1]==m and arr[-2]<arr[-1]:
        return len(arr)
    for i in range(len(arr)):
        if arr[i]==m and i+1<len(arr) and i-1>=0 and (arr[i-1]<m or arr[i+1]<m):
            return i+1
t = int(input())
for _ in range(t):
    n = int(input())
    arr = list(map(int,input().split()))
    print(domi_pira(arr))