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())
	l = list(map(int,input().split()))
	mx = max(l)
	t = 1
	for i in range(n):
		if i==0:
			if l[i]==mx:
				if l[i]>l[i+1]:
					print(i+1)
					t = 0
					break
		elif i == n-1:
			if l[i]==mx:
				if l[i]>l[i-1]:
					print(i+1)
					t = 0
					break
		else:
			if l[i] == mx:
				if l[i]>l[i-1]  or l[i]>l[i+1]:
					print(i+1)
					t = 0
					break
	if t:
		print(-1)