PCI = 3sss (0-167)+ PSS (0,1,2), so if you need to find the mode 3 values, shortcut way to divide pci by 3 and reminder is your mode 3 value. for and example if your PCI is 12 than 12/3= reminder 0 , so PCI mode 3 value is 0, same wayy for 13 is 1 and 14 is 2.
We have always 0,1,2 these 3 values of PSS in a site, so find the pss values for your whole market, plot in map info, use thematic and if same pss value sector is facing each other , than you need to change your PCI or swap the pci with in sector.
Well you can check your RACH failure KPI and throughput for the sector, if it is good and destance between the 2 sectors are high, you can live with that.