Adding a "filter" that will retain null results

I am trying to create a dashboard or report which lists all the counties in the system and their respective pull percentages (calculated as the pieces returned / pieces mailed). I can create this using summary, etc without an issue, but the challenge I'm facing is that I need to add a date range of the mail. Once I add the range to the filter, counties with no mail are removed. I understand that this is a database issue, not a metabase one, but I'm wondering if there is another workaround besides doing a manual SQL query and then using field filters in the join. (If I do a LEFT JOIN using the field filter on the date field, it works exactly as intended)

Any ideas? Thanks!