A detailed optical model of complex multi-layered structures of the separate-confinement-heterostructure (SCH) lasers as well as graded-index (GRIN) SCH lasers presented in the first part of the paper is used to discuss some of the possible modifications of their structure to reduce room-temperature thresholds. Recommended design parameters have been found for each structure. Surprisingly, performance of relatively simple SCH lasers is found to be at least comparable with that of much more complex GRIN-SCH lasers.