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

test_cases=int(input())
res=[]
for i in range(0,test_cases):
  no_of_places=int(input())
  a=list(map(int,input().split(" ")));
  equal=True
  for i in range(0,no_of_places-1):
    if a[i]!=a[i+1]:
      equal=False
      break
  if equal==True:
    res.append(-1);
  else:
    max=0
    index=-1
    for i in range(1,no_of_places-1):
      if a[i]>max and (a[i]>a[i+1] or a[i]>a[i-1]):
        max=a[i]
        index=i+1
    if max==0:
      if a[0]>a[1]:
        index==1
      if a[no_of_places-1]>a[no_of_places-2]:
        index=no_of_places-1
    res.append(index+1) 
for i in res:
  print(i)