Shadows: Rule 1 - Shadow Margin

Every graphic object, whether acting as a visible image or an invisible container, exists within a strict rectangular bounding box. If a shadow attempts to cast outside this box, it immediately hits the invisible wall and is clipped (cut off flat as shown in the middle image display).

Using the Formula ↔ No Formula Boundary Clips Shadow
Shadow Using Formula vs. No Formula
Shadow Dialog Using Formula Shadow Dialog Not Using Formula
Using Suggest to Calculate Margin
Shadow Using 'Suggest'
Shadow Dialog Using 'Suggest'