Thanks for the pics - smart looking car.
A couple of hours ago I started up and moved from cold a Series 2 CX 25 TRi Safari which had no problems starting at all and is the same engine...
Same with Roger's Prestige - also a 25 N/A Auto and that always starts up perfectly fine with no throttle needed from cold...
I'd go through the list Neil helpfully gave to find out what it is, or just live with it.
Sounds like a coincidence that both your and David's CXs have this slight issue - indeed they're all non-turbo cars.
An area for all matters concerning the Citroen CX.