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 hi(a):
	m = max(a)
	for j in range(len(a)):
		if a[j]==m:
			if(j-1)>=0:
				if a[j-1]<a[j]:
					return j+1
			if j+1<len(a):
				if a[j+1]<a[j]:
					return j+1
	return -1

t = int(input())
b = []
for i in range(t):
	p = int(input())
	a = list(map(int,input().split(" ")))
	# k = a[0]
	# c =1
	# for j in range(1,len(a));
	# 	if a[j]==k:
	# 		c+=1
	# if c==len(a):
	# 	return -1
	b.append(hi(a))
for i in range(len(b)):
	print(b[i])