I think DCA should be done more or less with the upward trend of cash flow as it allows to build up more bitcoin holdings in a short period of time.
Normally DCA is always done on a financial uptrend because that's when there will be a little surplus of money for the person to use and buy BTC and stack without looking back to whatever they are supposed to spend money on.
Having a downside cash flow will definitely minimise how much the person will have to spend on their expensive if it will even be enough to cover up daily expenses. Talk more about how much they care to spare to spend on DCAing Bitcoin.
Pardon me but I have not see this type of DCA approach that is only done on financial uptrend. The much I know is that DCA is a continuous buying method that is done irrespective of the market condition and the essence of the DCA method is to enable the investor plan the investment in a way that it will not have much financial burden on him that is why you buy small part of the funds per time and spread over a regular period of time. With proper planning, even during period of financial downtrend of the investor, the DCA method will be continued because the investor would have already figured out the funds for basic needs and also set aside emergency funds which serve as protection for the investment to prevent the investor from selling his asset unplanned. Therefore, the DCA is suitable for all market conditions and all income classes.