Given the entirely random placing of yellow lines across the network a blanket rule would be daft. Some are forward of the tactile paving, some are behind it, some are formed from the tactile paving, on several platforms I know parts of the yellow line allow about six inches of standing room behind them before meeting the back fence. The irony being of course that back in the day when there was a real risk of being whacked in the face by an opening slam door if you stood too close to the edge, most stations didn't have any yellow lines at all.