Phase: RAMIIVUncollided transmission at lower boundary level for direct illumination only
ftran_uc_dir for HET16_SRF_000_00 testcase.
ftran_uc_dir for HET16_SRF_000_20 testcase.
ftran_uc_dir for HET16_SRF_000_50 testcase.
ftran_uc_dir for HET16_SRF_090_20 testcase.
ftran_uc_dir for HET16_SRF_090_50 testcase.