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 math import *
import sys
from sys import stdin
from sys import stdout

input = stdin.readline

for __ in range(int(input())):
	n=int(input())
	a=list(map(int,input().split()))
	if(max(a)==min(a)):
		print(-1)
	else:
		m=max(a)
		for i in range(n-1):
			if(a[i]>a[i+1] and a[i]==m):
				print(i+1)
				break
			elif(a[i]<a[i+1] and a[i+1]==m):
				print(i+2)
				break

