Why gives NaBH4 more Felkin-Anh product than LiAlH4 gives? In lecture we discussed the nature of the nucleophile for the attack of the carbonyl.

LiAlH4 acts as a better nucleophile (hydride) than NaBH4. I know there is no hydroboration! So I would have expected that LiAlH4 gives more Felkin Anh product as the NaBH4 gives.

However LiAlH4 gives a Felkin Anh : Anti Felkin Anh ratio of 3:1 and
NaBH4 gives a ratio of 5:1.

detailed reaction
Source: Carreira, E.M.; Classics in Stereoselective Synthesis

Is there any good rational?
Lithium aluminum hydride is such a reactive nucleophile that it reacts readily with any conformation of the ketone. The reduced nucleophilicity of sodium borohydride allows for some discrimination of the conformations.

Note that the difference in selectivity between aluminum hydride and borohydride small. A large boost in stereoselectivity can be achieved by increasing steric bulk of the reducing agent (L-selectride gives a 10-fold increase in selectivity).