In simple words, if someone wants to invest for a long term or buy in dip and hold, then the total income must be divided into 3 parts. 50% daily expenses + bills and 20% Emergency & Reserve fund, that is, first complete the emergency, then create a reserve and the remaining 30% can be invested and this is the safest long-term investment plan. Now if you want, set up a DCA strategy with your profile for dip buying or long-term holding. If you keep it like this, it will be clear which money is for survival, which is as a buffer and which is for real investment. There are also many other strategies for investment, but this is the one I like the most and I consider it the safest.
We should invest based on our financial situation. As you said, 50% of the total income is daily expenses. How will you do if your daily expenses exceed 50% of your total income? Then your investment may be disrupted. You need to find a source of discretionary income. After that, how much % you invest depends entirely on you. Investing with discretionary income is best because you do not need this amount of money very much and your investment does not disrupt the continuity. The amount of money left after deducting all your expenses is your discretionary income. You can invest some amount of money from this discretionary income and create an emergency fund with some amount of money. For example, if your discretionary income is $200, you can allocate $100 for investment and $50 for emergency fund.
I think there is something we might call adjustment, we can always try to figure out our financial capabilities, and there is a limit that we can go to try and figure out our financial capabilities and then we can try finding out some adjustments concerning our level of discretionary income, because there is every possibilities that we might end up not accumulating and buying for the same amount on a weekly or monthly basis, because the bills might not exactly be the same number all week or months, but the income might just be the same number, that could have some effect on our discretionary income numbers, and you can actually try to adjust to some certain circumstances and cut down some of the expenses that could help generate more revenue of discretionary amount.