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()))
	ans, tp = -2, max(l)
	for i in range(n):
		if i==0:
			if l[i]==tp:
				if l[i+1]<tp:
					ans = i
					break
		elif i==(n-1):
			if l[i]==tp:
				if l[i-1]<tp:
					ans = i
					break
		else:
			if l[i]==tp:
				if l[i+1]<l[i] or l[i-1]<l[i]:
					ans = i
					break
	print(ans+1)