Mohr-Coloum plastic model

i am simulating a uniaxial test for coal specimen using Mohr-Coloumb plasticity, there is a friction between the coal sample and the platens, the coal behavior is stain sotening.

i want to know how many points should i use in the hardening table of the mohr-coloumb plasticiy to get a good reults?

 i used 3 points:- the first one is the yield stress and the associated plastic stain, the second one the peak stress and the associated plastic strain the third one is the post peak stress and the assoiacted plastic strain. is that right?