Lansky 8” kitchen knife (guided rod system)?

[wodahs]

Hello all - lansky’s website states that blades longer than 7” should be sharpened in sections and the vise would need to be adjusted using 2 fingers as a guide. Curious as to why this is - rods not long enough / angle change too great due to distance / something else? What experiences have people had with 8” knives and lansky? YouTube vids also seem to state that larger blades need the vise to be moved to sections - but none of the vids I saw state what length.

thanks!