G4hLowEnergyIonisation step length for low energy particles

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Hi, all!

In G4hLowEnergyIonisation process, why do we have a nonrandom step in the low energy range? Is there any physical reason for this, or is it just to minimise computational time?

My question concerns the piece of code that follows, which you can find in G4hLowEnergyIonisation.cc:

////////////////////////////////////////////////////////////////////////////
 if (fRangeNow > r) {
    stepLimit = dRoverRange*fRangeNow + r*(1.0 - dRoverRange)*(2.0 - r/fRangeNow);
    if (stepLimit > fRangeNow) stepLimit = fRangeNow;
  }
  // compute the (random) Step limit in standard energy range
  if(tscaled > highEnergy ) {

    // add Barkas correction directly to dedx
    fdEdx  += fBarkas;

    if(stepLimit > fRangeNow - dx*0.9) stepLimit = fRangeNow - dx*0.9 ;

  // Step limit in low energy range
  } else {
    G4double x = dx*paramStepLimit;
    if (stepLimit > x) stepLimit = x;
  }
  return stepLimit 
////////////////////////////////////////////////////////////////////////////