We see in some specific examples, that the K separation using the Trad Perfect Highlights screen, contain broken dots (see cake: shadow image). When using the Cdot, you don't have that much broken dots in the output.
Why this difference in result when using these two screens?
Traditional PerfectHighlight (=TPH) screens modulate tone by changing the number of dots. When this screen is used on high contrast highlights images, switching from one tone to another within the resolution of the image can cause a halftone dot to be removed or not. Furthermore, TPH screens also use dot repositioning or dance effect to reduce visibility of holes. This causes shifted fragments. When using AM screens changing from one tone to another just changes the size of a dot, and the dot remains on the orthogonal grid.
More broken fragments are visible when using FM screening compared to AM screening in highlights with lots of intensity variations.
Prevent noise in highlights
To prevent fragments that are too small to print properly, use in-rip dot removal (Dot Cleanup)