text: If the substrate has both an α- and β-stereocenter, the Felkin–Anh rule (1,2-induction) and the Evans model (1,3-induction) should considered at the same time. If these two stereocenters have an anti- relationship, both models predict the same diastereomer (the stereoreinforcing case).
  However, in the case of the syn-substrate, the Felkin–Anh and the Evans model predict different products (non-stereoreinforcing case).  It has been found that the size of the incoming nucleophile determines the type of control exerted over the stereochemistry.  In the case of a large nucleophile, the interaction of the α-stereocenter with the incoming nucleophile becomes dominant; therefore, the Felkin product is the major one.  Smaller nucleophiles, on the other hand, result in 1,3 control determining the asymmetry.