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())
	s=list(map(int,input().split()))
	if len(set(s))==1:print(-1)
	else:
		qq=max(s)
		for i in range(n):
			f=0
			if i and s[i-1]<s[i]:f=1
			if i+1<n and s[i+1]<s[i]:f=1
			if f and s[i]==qq:print(i+1);break