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())):
	n = int(input())
	l = list(map(int,input().split()))
	mx = max(l)
	cnt = l.count(mx)
	if len(l) == cnt:
		print(-1)
	else:
		for i in range(n-1):
			if l[i]>l[i+1]:
				print(i+1)
				break
			if i == n-2:
				if l[i]<l[i+1]:
					print(i+2)
