Volumetric standarization on Auto titration

As per internal SOP of volumetric Solution. The Standardize the volumetric solutions in triplicate and calculate the mean and Relative Standard Deviation and calculated molarity / normality should not differ from the prescribed strength by more than 10% and the molarity / normality shall be determined within a RSD of 0.2 %.

we have faced frequently problem to get 0.2% RSD in one time. i.e. every time we need to take LER and repeat the standardization. Also we have review Methrom Auto titrator manual, in manual they have find out RSD on 10 replicate instead of 3.

we have refer all pharmacopeia (USP/BP/IP) there is not mentioned regarding to replicate 3 or 6 or 10 preparation.

Please suggest way forward, Shall we perform on 6 or 10 replicate to get 0.2% RSD in one time?