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

test = int(input())
while(test):
	l = int(input())
	li = list(map(int,input().split()))
	mx= max(li)
	
	ans =0
	for i in range(l):
		if(li[i] == mx):
			if( (i == 0 ) and (li[i+1]<mx)):
				ans=i+1
				break
			elif((i == l-1) and (li[i-1]< mx) ):
				ans= i+1
				break
			elif((i < l-1) and ((li[i+1] < mx) or (li[i-1] < mx))):
				ans=i+1
				break
			else:
				ans=-1
	print(ans)

	test -= 1