SIP would have to consist of bars going across the inside of the door though mate.
I think the dents are to provide a minimalistic spring like action if the car was to ever end up on its roof. (believe me its possible :embarassed:) basically its a half figure of 8 chopped down the middle on the B pillar, as i said as far as i am aware it provides a structural "strong point" on the safety cage around the driver.