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

def piranha(a):
	biggest = max(a)

	c = -1

	for i in range(len(a)-1):
		if a[i]==biggest:
			if i!=0:
				if a[i+1]<a[i] or a[i-1]<a[i]:
					c = i+1
			elif i==0:
				if a[i+1]<a[i]:
					c = i+1
					break

	if a[-1]==biggest:
		if a[-2]<a[-1]:
			c = len(a)
	
	return c


n = int(input())
for _ in range(n):
	m = int(input())
	a = list(map(int, input().split()))
	print(piranha(a))