Sounds like you guys may be talking about different things. Are you talking about the initial setup of all the switches and settings that can be done by one pilot, or the response to the checklist where both have to check and reply? I'm not fluent in Airbusese, but I've taken "scan" to mean "flow," as in what's done from memory before the checklist. Am I right or wrong on this?
If it's the initial flow, I see no reason both have to be there.
If it's the final "checked" response after the crew has briefed the departure and otherwise gotten themselves on the same page regarding all the autopilot/navigation settings, etc. then obviously both have to be there.