1. The size arguments can appear out of order. See the example URL below.
2. Also, it's not the case that the first argument is always respected.

Try, for instance, this: https://lh5.googleusercontent.com/-rQ9SZ0dfJ_I/UtTzyqBufcI/AAAAAAAAOj4/zAOnrvu9aG8/w1280-s128-c-h720/Silver%2BLake%2BStarTrails.jpg
The arguments appear out of order but the URL does return an image.
The first argument is width 1280, but the size (128) argument applies.