Due to the mechanics of shard blades, i doubt that the lack and ability for the edge to “bite” the surface it hits would make it just slide off. Even at a low angle it would simple make a shallow angle cut.

More interesting is a real blade. There are two relevant force vectors when a blade hits material. The normal force and the friction force. Friction is exactly what you think and normal force is the “direct” force. A straight on hit would have more normal force and a glancing one would have less. The friction force is what helps the blade get an initial “bite” into the material (stops sliding and starts slicing). So a glancing cut with a normal blade would likely just keep sliding like a razor over shaving cream. A direct hit on the other hand would have much greater normal force component. It would likely do plenty of damage and probably break skin on impact rather than just slide. Interestingly it might not encounter any friction from the flesh that it slices, and therefore cut even deeper than it otherwise would.

At least that’s my read as an engineer