The 'Relative Date' filter is a wonderful tool, but limited by the way it is anchored, forcing users to either switch to 'Range Date' filters or build numerous calculated fields as workarounds to display data exactly how they want.
My suggestion is to add an 'advanced' option (so as not to take away existing functionality) with a relative start date and relative end date.
(example image for advanced relative dates below)
This will allow one to easily build date ranges such as:
- year to end of prior month
- last 13 months not including current month
- 6 prior and 3 upcoming months