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())

def checkio(arr):
	sorted_arr = sorted(arr)
	if (sorted_arr[0] == sorted_arr[len(arr) - 1]): return -1
	else: 
		for i in range(len(arr)):
			if (arr[i] == sorted_arr[-1]):
				if (i > 0 and i < len(arr) - 1):
					if (arr[i - 1] < arr[i] or arr[i + 1] < arr[i]): return i + 1
				elif (i < len(arr) - 1):
					if (arr[i + 1] < arr[i]): return i + 1
				else: 
					if (arr[i - 1] < arr[i]): return i + 1


for _ in range(t):
	n = int(input())
	aquarium = list(map(int, input().split(" ")))
	print(checkio(aquarium))