Well if I may, I'd like to add to the discussion. I present the information only to continue to promote the discussion, and not to determine the correctness of anyone's interpretations other than my own. Please consider these perspectives as I understand them.
For various reasons instructors have modified this technique and added unnecessary and thematically incorrect footwork, (Web of Knowledge). This technique is designed to make you consider various, but very specific ideas, and "stepping off line" is not one of them. The idea is for the technique to teach you to deal with a straight kick when you can only step backwards. Consider perhaps an environmental restriction such as a wall or table etc.
Stepping off line will take away the "Borrowed Force" componant of this lesson plan technique idea. Your opponent is supposed to "fall into" your elbow strike as he plants excessively forward from his kicking assault as you exploit the "defelction." There are other techniques that specifically ask you to consider "stepping off line for a straight kick at the next belt level. Traditionally techniques that use sophisticated avoidance footwork are explored further down the line. Stepping backwards is a more natural response for a beginner. (Remember a person is going from no training to this technique)
The technique is named "Deflecting HAMMER" because it wants you to learn to utilize what is called a "complimentary downward block," not a parry. A Parry "rides and redirects." A "defelection is predicated on the Angle of Intersection which may vary from an Angle of Incidence (right angle) up to the angle where it no longer deflects and becomes a parry. Parry is a subcategory of a block. Blocks "check or hinder" by definition. Further, the hand is "closed" in a "hammer" position to protect the fingers at that level, thus the name of the technique, "Deflecting Hammer."
In my teaching we also consider the "Double Check Factor" as soon as a student is capable of assimilation of the technique specific information, utilizing both hands in the execution. Executed properly this technique is quite effective, but care and time must be factored into a students learning to effectively execute it.
Changing, or failing to consider any of the above factors does not make the technique NOT Deflecting Hammer, but it will change the lesson plan significantly and suggest alternative information while missing significate lessons to be learned from the Web of Knowledge Lesson Plan Theme of the technique.
Respectfully,