Where there is close interaction between Circular (C) dot and Circular Samba (CS36), a noticeable transition point is found in the screened result as seen in BitMap Viewer.
Where you normally use Circular dot for all Inks, in some cases, you may apply Circular Samba to some objects to soften the edges of shadow images.
Checking the Screens and DGC details of the TIFF or LEN and see that Circular and Circular Samba are produced at slightly different screen Rulings.
From Esko FIQ:
"CS screens are built from a completely different screen tile from Circular. … use CS4 instead of Circular. The 4px Samba screen will be exactly like Circular in the highlights".
To resolve this, use Circular (CS4) instead of Circular for the overall screening, then apply Circular Samba (CS36) to where needed. The 4px Samba screen will be exactly like Circular in the highlights and since both CS screens from the same tile, you will get a clean transition.
An alternative solution is to use Screen Manager to create a new screen, based on the Circular dot, with the effects (in the highlights and/or shadows) you want. As the new screen is based on the Circular dot too, rulings will match exactly.