VDS kept around 15 and 20 mg of mixed harmalas per ml of total liquid (water + acid), then he start to base.

If you rise concentration the freebase precips get more sticky on the vessel walls, pH probe etc (especially using carbonates to base then it can get messy).

If you lower concentration then the pH depressions get fainter and flatter, the separation becomes thus more difficult to pin point.

One does not have to follow VDS mechanics by any means, things will precipitate under any base and a wide range of concentrations eventually. Though it will happen without pH depressions as handy indicators.