Due to the wraparound effect, the lag difference is zero.
That's because the lag gradient vertically shifts and when it wraps around, it realigns back to the way it was -- back to square one.
At strobe phase 100 the strobe flash delayed by one frame, means the previous strobe flash and next strobe flash is also delayed one frame. You're back to square one. Consider the refresh cycle like an infinite loop. It's the same thing if you fly around planet Earth, cross the international Date zone, and land back here -- in an orbital rocket in less than 24 hours -- and it's still the same day if you land here at this same very location -- the wraparound effect.
The latency is constant at the top edge and bottom edge of the crosstalk zone and the lag gradient "follows" the crosstalk zone, and the top/bottom edges wraps around to each other.
Phase 0 and Phase 100 has a slight difference in crosstalk bar location so it really corresponds to roughly a 95% phase adjustment range, but the lag relative to crosstalk bar is exactly identical for all possible crosstalk bar positions, whether or not it's wrapping around to the opposite end of the screen. Basically the input lag 1 inch above the crosstalk bar is the same for all crosstalk (strobe phase) settings, regardless of the crosstalk bar position.
Even though it shifts ahead/back by 1 frame in the simulation, the lag isn't shifting 1 frame ahead/back. In reality, the image is in motion so any shift forward is compensated by increasing lag. Eventually when crosstalk bar reaches near the bottom of screen, the lag of the top edge is now resembling the lag right underneath the crosstalk bar, so that 1 frame shift "ahead" is now cancelled out by 1 frame lag behind (see latency gradient diagram), resulting in same as before -- meaning crosstalk 0 and 100 has darn near the same lag. If this was photographed in absolute time, there would be no shift, but the shift is showing up in this animation simply because it's a simulation on a static image, rather than a scrolling image in motion.
For more information about strobe latency with Crosstalk adjustments, see ANIMATIONS: Adjusting Strobe Phase & Crosstalk