Sitting closer you reduce some of the reflections.
It’s important to consider how far the speakers are positioned from the front and side walls, how far are they apart and the distance between listening chair to the back wall.
Size of the room, any openings to either or both sides, room acoustics treatments, etc.
What Wilson states in the manual is good as a guideline.
If closer or further works better for you, then that’s your optimal set up.