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())
	r = [int(i) for i in input().split()]
	o = max(r)
	if r.count(o)==len(r):
		print(-1)
		continue
	kq = -1
	for i in range(1,len(r)):
		if r[i]==o and (r[i]>r[i-1]):
			kq = i+1
	for i in range(len(r)-1):
		if r[i]==o and(r[i]>r[i+1]):
			kq = i+1
	print(kq)