Are there concentration effects in enantioselective deprotonation of cyclic ketones?

Deprotonation of tropinone and its sulfur analog (8-thiabicyclo[3.2.1]octan-3-one, TBON) with chiral lithium amides (e.g. lithium N-benzyl-α-methylbenzylamide), followed by addition of the resulting enolates to benzaldehyde, affords non-racemic products, the enantiomeric excess of which depends on the concentration of the lithium amide.