I notice that when looking this up on the fare finder provided by LTFares.com, Tooting Broadway to White City is priced using the tube (LU) mode for all possible journeys, while Tooting Broadway to Shepherds Bush NR includes the more expensive £2.90 peak “Avoiding Zone 1 via Balham and Clapham Junction” route, for which it lists the price mode as “national-rail”.