When difficulty is set to A, the Zorlon Cannon will destroy the Destroyer Missile if it hits it (instead of passing through it), and the Swirl will move much faster.
Let my WIP play out and then do nothing. The Swirl will begin to attack on frame 1379. The Swirl will attack in a straight line, which usually means x decreases by 4 pixels per frame. The Qotile's x value will display:
It visibly moves on every frame, but every 6th frame the value isn't updated in $2A. If you toggle the L difficulty before frame 1379, the x value displays:
It displays the same odd behavior where the x value doesn't change every 6 frames, despite moving visually, but now it finishes crossing the screen on frame 1424 instead of 1409. Difficulty B = 4 pixels/frame, Difficulty A = 6 pixels/frame (+50%).
Incidentally, when I made my WIP, I had to make the Yar follow the Zorlon Cannon from above it instead of below it to prevent the Destroyer Missile tracking Yar downwards and crossing the Cannon's path, destroying it before it hit the Swirl.