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())
	arr = list(map(int,input().split()))
	maxx = max(arr)
	if arr[0]==maxx and arr[1]!=maxx:
		print(1)
	elif arr[-1]==maxx and arr[-2]!=maxx:
		print(n)
	else:
		ans = -1
		for i in range(1,n-1):
			if arr[i]==maxx and arr[i-1]!=maxx or arr[i+1]!=maxx:
				ans = i+1
				break
		print(ans)