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 *
from collections import *
from itertools import *
from functools import *
from bisect import *
from heapq import *
from operator import *
from sys import *
setrecursionlimit(100000000)


for _ in range(int(input())):
	n=int(input())
	l=list(map(int,input().split()))
	if l==[l[0]]*n:
		print(-1)
		continue	
	x=max(l)
	ans=0
	for i in range(n):
		if l[i]==x:
			if (i!=0 and l[i-1]!=x) or (i!=n-1 and l[i+1]!=x):
				ans=i+1	
				break
	print(ans)
	