ZOR Antenna Surface Finish

Hi,

AN-B-027 application note presents antenna designs and matching component values for each antenna.
它说这些值基于“增大化现实”技术e PCB thickness and enclousure material dependent. But it says nothing about PCB surface finish.

I've found in this forum and in RefDes documentation that the proposed surface finish for IFA antennas is solder mask over bare copper.
But I am confused about surface finish for ZOR antenna. On the photos in AN-B-027 all antenna area looks solder mask free with ENIG finish.