Thanks for that clarification. Scale to fill, and the options for scaling (I think), were added with CS6. But even in CS6, you can't set Encore to use the scale to fill when handling HD to SD using the automatic setting.
Edit: in PR, prior to CS6, you could accomplish the same thing by enabling source cropping. But there was a bit of discusson about the right number of pixels to crop.
Even though the above discussion is about AME/PR, you can do the scale to fill in Encore as long as you are not using the automatic setting. But the preferred work flow for many users is to bring the ready to use assets into Encore.