For the premium service the limit is 2000. You can use 'post' instead of 'get' to avoid the url length limit, you should also round the coordinates to some meaningful number of digits (5) to avoid passing unnecessary bytes.
It is a mixture of both. The number of parameters passed and the numbers of tiles that had to be looked up. The number of tiles count a lot more and in your example it will be a little more than one point (depending on how many points you have passed).