Problem with Modbus serial repeaters

I am working in a project using premium PLC as a master to control 10 Zelio slave PLCs, the Zelios are far apart from the premium PLC so I used 2 repeaters (Phoenix Type) and arranged the repeaters according to the distances (not to be more than 1200M) the repeaters contain internal terminating resistors I changed the terminating resistors position and each time some RTUs can't be detected , the best case I detected 9 zelios but still one not deteceted

Please send me the right configuration of the terminating resistors for this application