Holding back available money with intention of using it up gradually in DCA approach is so wack. You have an available funds, instead of investing it you now spread it along still in fiat, that's a financial mistake already. The said fiat money is vulnerable to devaluation weekly if not daily. Same amount may never get you equal amount of bitcoin in the next DCA period. DCA is planned with your next possible discretionary income to enable you make good application of the money without avoidable financial losses or unnecessary spendings. You can choose to hold for dip sake which is not also guaranteed to happen. But the best practice would be channelling such money into aggressive buys if you're sure to have taken care of all your responsibilities and saved your emergency funds and back up funds.
Yes, you are right. We should never hoard our available discretionary money for investment. Rather, being aggressive in investing with that money should be a good use of money. In this case, you need to ensure that it is prudent money and you have adequate backup (emergency fund, reserve fund, floating fund and required funds) funds. In such a situation, if you have selected the extra money for investment, then do not keep it in fiat or stable money for a long time. Because you may miss out on good opportunities to buy.
For DCA, you can depend on a regular source of income and you can determine the duration of DCA depending on the source of income. If you have extra discretionary funds outside DCA, then it may be a good move to be aggressive in investing immediately with that.