Hello,
According to specs, the Plus version of CLRC663 has an improved output current on the transmission, which is called ITVDD, where ITVDDmax = 350 mA under loading conditions. In theory, if you switched the Frontend from the "Not-Plus" to the Plus version, you will not notice any improvement since the matching has been done for the same target impedance, in this case for the previous CLRC663.
It would be helpful to please refer to the Antenna design App Note for reference about changing the target impedance for better performance: https://www.nxp.com/docs/en/application-note/AN11019.pdf
Hope this helps!
BR,
Ivan.
