Hi Sing Yan Ang,
What you're trying to achieve is to filter
only those months (in both FY2019 & FY2018)
that are equal or less then the highest Fiscal Month
(number) available in the data (in the chosen FYs).
This could be done easily via a LOD expression.
Other things are just plain simple (you did it).
Please find the attached.
Thank you so much!