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 = [int(i) for i in input().split()]
	dom, f, ans = max(l), False, False
	for i in range(n):
		if l[i] < dom:
			f = True
			break
	if not f:
		print(-1)
	else:
		for i in range(1, n):
			if l[i] == dom and l[i] > l[i-1]:
				print(i+1)
				ans = True
				break
		if not ans:
			for i in range(n-1):
				if l[i] == dom and l[i] > l[i+1]:
					print(i+1)
					break