Proper value for FERROR ? (EtherCAT Servo)

I want to trigger an error if the difference between the actual servo position and the commanded position exceeds a certain threshold (e.g., 5mm) due to external forces. However, unless I set the in the .ini file JOINT section to something very large (like 50 or 500), a 'Following Error' occurs immediately.

= INI FILE =[JOINT_0]
MIN_FERROR = 500
FERROR = 50

I want to set these values to be able to check following error within 5mm (5.0mm)
 I have already tuned the SERVO gains appropriately and confirmed that the actual physical deviation is nowhere near 50mm. The servo's electronic gear is configured so that 1 unit equals 1/1000mm, and I am converting the values to integers before writing them to EtherCAT.

= HAL FILE =
setp cia402.0.pos-scale 1000
 I know threre are 1ms time difference in EtherCAT and latency for servo position, but I think these settings are not proper.

Which part of LCNC settings should I check or modify to resolve this problem?