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())
	l=list(map(int,input().split()))
	j=set(l)
	if len(j)==1:print(-1)
	else:
		k=max(j)
		for x in range(n-1):
			if l[x]>l[x+1] and l[x]+1>k:
				print(x+1)
				break
			elif l[x]<l[x+1] and l[x+1]+1>k:
				print(x+2)
				break