The cubic B20-type (space group P213) compound Mn_(1-y)Fe_(y)Si with y = [0; 0.15] order in a spin helix structure with a small propagation vector 0.36 < k < 0.70 nm^-1. The critical temperature of the compounds T_C decreases with the Fe doping and approaches zero, discovering the quantum phase transition (QPT) at y_C ≈ 0.15. Mn_(1-y)Fe_(y)Si undergoes a transition from a paramagnetic phase (P) passing a partially chiral fluctuating state (PCF), followed by a highly chiral fluctuating (HCF) state resulting in a stable spiral (S) state at T_C. The magnetic properties at the transition from P to PCF are clearly related and perhaps determined by the value of the correlation length of critical fluctuations and the value of the spiral wave vector, which increases significantly upon doping from 0.36 nm-1 to 1.00 nm^-1. The proposal is aimed to study in details the character and changes of the thermal phase transition upon its way to the quantum critical point at y_C ≈ 0.15 0.17 by means of polarized small angle neutron diffraction (SANS). The measurements would be crucial for revealing the true nature of the QPT.