An important challenge for ns-3 is to enable efficient performance evaluation of increasingly dense and heterogeneous networks, cognizant of cross-layer (specifically, Layers 1 & 2) interactions. In this work (a continuation of U. Washington efforts), we present improved physical layer abstractions for a key component underlying all 802.11 WLAN MAC performance evaluation - the Clear Channel Assessment (CCA) procedure central to CSMA/CA - for implementation in the ns-3 simulator. We model the preamble correlation process as typically implemented in 802.11 radio and represent the resulting probability of detection as a look-up table with a parameterized correlation threshold for different receive sensitivity strategies. Further, we also added a new carrier sense threshold adjustment mechanism to allow nodes to enable bypassing the default (and to date, fixed) -82dBm threshold. Such a capability aligns ns-3 for performance evaluation of dense networks equipped with new spatial reuse mechanisms. We demonstrate this via simulation of spatial reuse gains from dynamic sensitivity control (DSC) that are verified against IEEE 802.11ax standards group contributions. Using simulation results from a fixed rate multi-BSS network, we then identify valuable design guidelines to maximize the aggregate throughput with DSC.