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

from sys import stdin
nii=lambda:map(int,stdin.readline().split())
lnii=lambda:list(map(int,stdin.readline().split()))

t=int(input())

for i in range(t):
  n=int(input())
  a=lnii()

  if len(set(a))==1:
    print(-1)
    continue

  mv=max(a)
  for i in range(n):
    if a[i]==mv:
      if i-1>=0 and a[i-1]!=mv:
        print(i+1)
        break
      if i+1<n and a[i+1]!=mv:
        print(i+1)
        break