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())
	lis = list(map(int, input().split()))
	if max(lis)!=min(lis):
		idx = lis.index(max(lis))
		i = idx
		while i < n-1 and lis[i] == lis[i + 1]:
			i += 1
		if i >= n-1 :
			i = idx
			while i >0 and lis[i] == lis[i - 1]:
				i -= 1
		print(i+1)

	else:
		print(-1)