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

for _ in range(int(input())):
   n = int(input())
   a = list(map(int, input().split()))
   mx, mn = max(a), min(a)
   if mx==mn:
      print(-1)
      continue
   ind = a.index(mx)
   if n==2:
      print(ind+1)
      continue
   
   for i in range(ind,n):
      if i>0:
         if a[i-1]<mx:
            fl = i
            break
      if i<n-1:
         if a[i+1]<mx:
            fl = i
            break
      
   print(fl+1)
   
