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 solve(n,arr):
  maxx=max(arr)
  for i in range(len(arr)):
    if arr[i]==maxx:
      if i==0:
        if arr[i+1]<arr[i]:
          return i+1
      elif i==len(arr)-1:
        if arr[i-1]<arr[i]:
          return i+1
      else:
        if arr[i-1]<arr[i] or arr[i+1]<arr[i]:
          return i+1
  return -1
        




  





for i in range(int(input())):
  n=int(input())
  arr=list(map(int,input().split()))

  print(solve(n,arr))