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

t = int(input())
for _ in range(t):
	n = int(input())
	arr = [int(j) for j in input().split()]

	if arr.count(arr[0]) == len(arr):
		print(-1)
		continue

	ma = max(arr)

	for i in range(1, n):
		if arr[i] == ma and arr[i-1] != ma:
			ans = i
			break

	for i in range(n-1):
		if arr[i] == ma and arr[i+1] != ma:
			ans = i
			break

	print(ans+1)