Qlik Sense 30 Day calculation ignoring date filters

Hello,

I am currently using the following formula:

RangeSum(Below(Sum(Aggr(FLIGHT,FLIGHT_KEY)),0,30))

In a table that I have in the visualisation I can show the date in the first column, the number of FLIGHTs for that date in the second column, and in the third column, the above formula shows the sum of the last 30 days of FLIGHTs. My problem is, if I apply a filter for a month, the first 30 days of the month don't include the last 30 days as the previous month is filtered out. How can I force the formula to include the 30 days before the first date of the filtered range?

I assume I need a {1} or a Total somewhere in there, but I have not had much success.

Thank you.