It start with available finance, reserved emergency fund, and investment capital. Without good finance, without reserved emergency fund, investors will have more risk of unavoidable sales even the market is not good, and the investment portfolio is in loss temporarily. If they can manage their finance well, they will very less likely have to sale off their bitcoin. It will help them holding their bitcoin more strongly and don't have to sell it at loss just because they urgently need money.

Your math works rightly but big conditions written above must be prepared well. DCA strategy for investment is good, but if everything starts without enough careful and detailed plans, financial, capital and risk management, this strategy can not help.