In openairinterface5g many definitions in many layers of UE or eNB NB_MAX. We created a file called openairinterface5g_limits.h located at openairinterface5g_dir/targets/COMMON/ declaring the number max of UE and eNB to be used in ALL layers depending on launching conditions (LARGE_SCALE for example).
This the driver for the UE when NAS layer is running in the UE (EPC setting).