We use polarized neutron reflectometry and dc magnetometry to obtain a comprehensive picture of the magnetic structure of a series of La(2/3)Sr(1/3)MnO3/Pr(2/3)Ca(1/3)MnO3 (LSMO/PCMO) superlattices, with varying thickness of the antiferromagnetic (AFM) PCMO layers (0<or=tA<or=7.6 nm). While LSMO presents a few magnetically frustrated monolayers at the interfaces with PCMO, in the latter a magnetic contribution due to ferromagnetic (FM) inclusions within the AFM matrix is maximized at tA approximately 3 nm. This enhancement of FM moment occurs at the matching between layer thickness and cluster size, implying the possibility of tuning phase separation by imposing appropriate geometrical constraints which favor the accommodation of FM nanoclusters within the "non-FM" material.