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

t=int(input())
for _ in range(t):
	n=int(input())
	l=list(map(int, input().split()))
	if len(list(set(l)))==1:
		print(-1)
	else:
		i=l.index(max(l))
		j=i+1
		while(j<n and l[j]==l[i]):
			j+=1
		if l[j-1]==l[i]:
			j=i+1
		print(j)
