Buying low and selling high is a simple strategy but then the price direction is highly unpredictable, so your analogy may not be accurate at all times since Bitcoin price cant is predicted, ask yourself what if the price goes opposite what you proclaimed in your trading strategy.
Am not a passive trader any ways am more of a holder than a trader and i will say it is better to buy low and hold for long time and again ops that your 30% calculation is inaccurate considering Bitcoin present position.
In the current bear market, what we assume is actually the opposite. As a result our portfolio keeps decreasing day by day. So I think at this time it is better to invest small amount consistently by monitoring the market well. It is best to exercise maximum patience to keep your portfolio safe. It is wise to invest when the market is at its highest lows.