The DCA amount does not need to be the same amount, and the DCA amount and the regularity of such investments could strictly be based upon when a person has a certain level of discretionary income that is upon his own choosing in regards to reaching such thresholds, so even relatively modest amounts of investing into bitcoin could end up paying off quite well in the long term, as long as the investor also understands that investing can sometimes take time to play out.
I really feel there should be a base amount when DCAing, sort of an amount you should not go below, so as to put yourself in check and foster continued discipline and commitment in your investment. This comes from the knowledge that the human mind is cunny and can overly adapt to a pattern and possibly exploit it to the disadvantage of the individual, so for example, If you set a base, lets say $50 and you know that you can afford it weekly as a minimum, at some times when you have more cash with you you can invest $70, $100 or even more provided you have made accurate plans for the next week's minimum of $50 to fall in place. you are better off than someone who invests $200 this week and possibly $20 next week, $30 in two weeks time as he can even decide not to invest in a week citing and deceiving himself that he has invested much previously.
This will help you become more disciplined and consistent investor over a long period of time as against investing randomly without an investment guideline for yourself and the guidelines would help you succeed in your investment journey with ease as it tends to be part of you overtime and as a committed investor, the more your earnings increase, the more you raise the bar on your minimum investment and the more bitcoin you would accumulate over a long period of time.