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 " "*int(input()):
  n=int(input())
  a=list(map(int,input().split()))
  if len(set(a))==1:
    print(-1)
  else:
    mx=max(a)
    f=0
    for i in range(1,n-1):
      if a[i] == mx and (a[i] >a[i-1] or a[i] > a[i+1]):
        print(i+1)
        f=1
        break
    if f==0:
      if a[0] == mx:
        print(1)
      else:
        print(n)