I am not aware of a direct reference to a BR's final step; however, it is understood that the BR must be given an opportunity to touch 1B in some way.
If you want to get technical, the foul line (inside part of the runner's lane) does run into the front side of 1B, so the BR would be allowed that area of the bag to touch 1B.
There's no reason to be that technical though. It's about fairness. Normally runner's lane violations are due to the BR being in the way of a throw coming from behind him (from the area of home plate or 1B foul line). Also note, FED does not require a quality throw for RLI to occur.