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 i in range(int(input())):
	n=int(input())
	l=list(map(int,input().split()))
	cnt=0
	l1=sorted(l)
	a=l1[-1]
	for i in range(len(l)-1):
		if l[i]>l[i+1] and l[i]==a:
			cnt+=(i+1)
			break
	if cnt==0:
		for i in range(len(l)-1,0,-1):
			if l[i]>l[i-1] and l[i]==a:
				cnt+=(i+1)
				break
	if cnt==0:
		print(-1)
	else:
		print(cnt)