[Psionic Powers] With an Expanded PK Shield, when do rolls occur?

[DangerousThing]

I would do what the book says.

You roll at a -5 (unless you've bought up the technique), and if you succeed, you protect a 2-yard area (or more, double for each multiple of 5 you make the roll by).

Whenever the shield is hit, you roll against your unmodified skill. At least it isn't modified by the technique, but it might be modified by other things (like have other PK powers running).