You can narrow your search down even more by specifying a value square to target. All word positions in the result will contain this square.
Because we are dealing with such a massive amount of data (the scores of all words at all board positions), we only return a fraction of all possible plays, and only the highest scoring plays. Otherwise, your devices would come to a grinding halt just from the sheer volume of data.
For example, if you are specifically looking for something to hit a triple word score, and we return 3000 plays to you, without specifying this premium square, these 3000 plays might only contain 20% of what you are interested in. If you select it, all 3000 plays will contain a triple word placement (if indeed there are 3000 plays with the triple word placement to be had, fewer if not).
The score of a word in Words With Friends™ depends both on the value of the letters and the value of the squares on which you play those letters. You do not get an accurate sense for the value of a word just by adding up the letters. A word can have drastically different scores at different board positions. A three letter word played right might have a higher score than a seven letter word, but without the 50 point bonus. In order for you to cash in on the premium squares, you must be the one to play the letter on those squares. If not, your score might be somewhat less than our predicted value. You can increase your score for a word even more by extending or playing parallel to previously played words. There are many things that determine the real value of a played word. It is not a trivial game. The scores of all words in a growing list at all board positions we can calculate, and it is a massive amount of data. Some things we can't predict, and this is why we love the game.