Thanks for the reply C Star.
My experience so far is only in long haul and ETOPS ops, as I toiled away in GA prior, hence my questions. Where I work now we operate our medium-long haul flights much the same in that they are always ETOPS flights, regardless of the presence of numerous adequate airports within 60 min.
I have however observed a regional Asian flight of about 4 hours. The CFP didn't contain any enroute alternates and no crit point info was included. I assume additional airports were used to calculate the depress and OEI fuel scenarios as without you'd be looking at about 2 hours depress. Unless of course I'm wrong and the departure and destination did cover all scenarios. I just found it interesting there was nothing published regarding diversion calculations.