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())
	a = list(map(int, input().split()))
	m = max(a)
	res = 0
	for i in range(n):
		if a[i] == m:
			if i == 0:
				if a[i+1] < m:
					res = i+1
					break
			elif i == (n-1):
				if a[i-1] < m:
					res = i+1
					break
			elif a[i-1] < m or a[i+1] < m:
				res = i+1
				break
		# ~ print(i)
	print(res if res else -1)
				
				
