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.