I weekly commute to CDG. They are not separate terminals any more. Think of them as B Gates and D Gates inside the same building. They share a common security screen and a common immigration zone. Both have small Schengen zones that sub divide the Gates. The BA checkin desks are on the 'D' side of the security area but used to be on the 'B' side of the security area. It makes no difference. Equally no difference which gate you arrive at because they all feed the same immigration area.

You can relax