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

if __name__ == "__main__":
	t = int(input())
	for i in range(t):
		n = int(input())
		arr = list(map(int, input().split()))
		maxx = max(arr)
		if len(set(arr)) == 1:
			print(-1)
		else:
			ans = []
			for i in range(len(arr)):
				if arr[i] == maxx:
					arr[i] = 1
				else:
					arr[i] = 0
			for i in range(len(arr)-1):
				if arr[i]==0 and arr[i+1]==1:
					ans.append(i+2)
				elif arr[i]==1 and arr[i+1]==0:
					ans.append(i+1)
			print(ans[0])
