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())
	a=list(map(int,input().split()))
	s=set(a)
	if(len(s)==1):
		print(-1)
		continue

	mx=max(a)
	for i in range(n):
		if(a[i]==mx and ((i!=0 and a[i-1]!=mx) or (i!=n-1 and a[i+1]!=mx))):
			ans=i+1
			break

	print(ans)
