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 range(int(input())):
	x = int(input())
	mylist = list(map(int,input().split()))
	amr = dict()
	for i in range(x):
		if i ==0  and mylist[i+1] < mylist[i]:
			amr[mylist[i]] = i
		elif i == x-1 and mylist[i-1] < mylist[i]:
			amr[mylist[i]] = i
		elif i >0 and i < x-1:
			
			if mylist[i-1] < mylist[i] and mylist[i] >= mylist[i+1]:
				amr[mylist[i]] = i
			elif mylist[i-1] <= mylist[i] and mylist[i] > mylist[i+1]:
				amr[mylist[i]] = i
	mx = -1
	if amr :
		mx = max(amr.items())
		print(mx[1]+1)
	else:
		print(mx)