I see where someone else suggests the exact opposite. Current behavior of WordChums version does add bonus for 5,6, and 7 letter words.

The problem is...wordchums plays, the vast majority of the time, cover some multiplier bonus which multiplies only the letter score, not the additional word length bonus. So predicting the final score requires first figuring out what annagrammer added to the letter score, subtracting that, applying the multiplier, and then adding the length bonus. Much easier if only the letter score is counted by annagrammer.

I've come here from wordfinder, which has gone nutty of late, tightlooping, taking GB of ram, locking up, but they do this one better.