Shields were all about the slowstab. The shield would help to make the slow blade unbreakable. the very simplest were a flat plane. most others had to be some sort of deformed bubble, sealing against the ground usually. a half-shield was folded back into itself instead of over the werer and the ground, like two domes inside each other. The relevant articles in the Dune encyclopedia are very good, and I don't think any texts contradict the physics they present (in OH or BH/KJA).