This is more of a theoretical point than a practical one, since it is extremely improbable that you would be able to locate the exact same quantity of inventory each month and sell it all inside the month. Additionally, the numerical values utilized are arbitrary.
You may adjust the source budgets as necessary to make them work for your particular circumstances. Simply redo the calculation. While this is somewhat speculative, I think there is actual benefit in examining the preceding scenario when determining the necessary ROI for product sourcing.
Now, a few observations on the preceding instances.
To begin, if you reach a point where you are happy with your earnings and hours worked, you should never contemplate lowering your ROI in order to raise your income.