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()))

	mxp=[0]*n
	mxs=[0]*n

	ans=-1

	mx=0
	for i in range(n):
		mxp[i]=mx
		mx=max(mx-1,a[i])

	mx=0
	for i in range(n-1,-1,-1):
		mxs[i]=mx
		mx=max(mx-1,a[i])

	for i in range(n):
		if (a[i]>mxp[i] and a[i]+i>mxs[i]) or (a[i]>mxs[i] and a[i]+(n-i-1)>mxp[i]):
			ans=i+1
			break

	print(ans)