Travelling soon from BKK with Gulfair, can someone explain how the concourse system works for int’l flights works? Can you pass between the concourses after security or are you limited to where your flight departs from?

Reason I ask is I have option of two lounges; Gulfair says access to Louis Tavern CIP on third floor (is there a difference between First and business as their website sells access and implies it is one and the same), or AirFrance KLM on concourse G third floor. Is any one better?

Tried to work out where Gulf depart from and looking at the departures from last week it’s been seemingly random.