An improved coupled-mode theory is used to analyse various phase-coupled, index-guided diode laser arrays. Different designs of 10-guide arrays are considered,including uniform, linearly chirped, Λ-chirped, V-chirped, and saw-tooth arrays. Lower-order supermodes are favored when there is excess gain between the guides. However, a common problem with large arrays is the relatively poor mode discrimination. This can be remedied by proper gain tailoring, which results in significantly higher gain for the lowest-order supermode. Further improvement can be achieved with moderately strong coupling, when the highest-order supermodes can be made cut-off, thus reducing mode competition due to spatial hole burning effects above threshold.