I consider DCA to be way more flexible than you are making it out to be. You could have DCAs that are very aggressive and approach the use of 100% of your disposable income for buying BTC whenever the money comes in or you can make a weekly determination.
You could also set up DCA to be automatic and a very low number such as $10 per week (and maybe your disposable income is $1k per week, so you pick a real low and whimpy number such as $10 per week, or you could pick a more aggressive number. Of course the more aggressive you are, then the more careful you need to be that you don't overdo it and make mistakes and being more aggressive likely justifies having a more solid system of emergency and back up funds in place in order to rescue you if .you go to far in regards to your DCA or if you miscalculate and end up spending outside of your disposable income and from money you need for your expenses.
I always welcome this kind of strategy.
I myself always try to invest the smallest amount of my income in the DCA scheme. Sometimes it is $10, sometimes $20, sometimes $5. So that I will not make any impact on my financial situation.
And I also think that it is wiser to invest more to hold more, not leave funds to cover emergency situations, and then sell some of the bitcoin holdings after facing an emergency situation.
So small fund but for long-term strategy would really helpful as it is also risks management skill.
And We must not forget that-
"
Little drop of water,
Little grains of sand,
Make the mighty ocean,
And the pleasant land"