There is also what is called hyper DCA, this method is a kind of pattern that one can buy bitcoin anytime and not with a certain amount of money, just like the way MicroStrategy buys his bitcoin. For you to know that he is DCAing is when you add all the bitcoin that he has bought together, and how many years he has used to buy them. This will give you the average price by month or annually.
Buying Bitcoin at any amount at different intervals without it being the same amount is also good but it is better to use the regular DCAing of same amount at different periods of time because it will enable the investor to be more active and effective in the DCA but for an investor doing irregular DCAing, they might not take it seriously since they feel they can buy at any time they want to but for someone DCA same amount, they are more disciplined and are more likely to get huge accumulations since they are always consistent in their DCA amount.
There are reasons some people do not maintain the same amount which is the DCA method you are describing. It could be a case of cashflow variation in which the investor does not have regular cashflow, sometimes bigger amount and sometimes smaller amount. This way the investor can buy in accordance to how the money comes instead of maintaining the same amount of money. I don't have a problem with this time of approach even though I'm still using the DCA method.