If a substance dissolved in the solvent is absorbed very poorly. It has far reaching. The substance dissolved in the solvent can not be absorbed very near the beginning.
If the substance that dissolves in a solvent to absorb the good bad and thus move. Best substances dissolve in the solvent is not good is a good absorbent, so close to the start point.
If the substances dissolved in the solvent is absorbed better, so it doesn't have to move far away and dissolved substances in solvent was not good to be absorbed, so it is near the starting point.