Solvent vapor annealing (SVA) has been shown recently to be an effective means to produce long-range lateral order in block copolymer (BCP) thin films in relatively short times. Furthermore, using substrates with faceted surfaces allows for generating unidirectional ordering of BCP microdomains on the size scale of an entire wafer. While in recent years SVA has been greatly demystified, the detailed pathways toward obtaining unidirectional order still remain unclear. Grazing-incidence X-ray scattering (GISAXS) is a very powerful tool for characterizing the structure and morphology of BCPs in thin films, and is particularly useful for studying structural changes in BCP thin films during SVA. We here present in situ GISAXS experiments of cylinder-forming PS-b-P2VP BCP thin films on faceted Sapphire substrates during annealing in THF. We show that the directional order of cylindrical microdomains is greatly enhanced at solvent concentration close to the order-disorder transition of the copolymer. Furthermore, we observed that inducing disorder by further increasing the solvent concentrations and subsequent quenching to the ordered (not yet glassy) state induced the highest degree of directional order with nearly unidirectional alignment of the microdomains. Additional constraints can be placed on the lateral ordering intramlecularly by varying the topology of the BCPs.