Help with rolling 12 month as of table

[7KD]

Hi, i have created an asoftable as per https://community.qlik.com/t5/Design/The-As-Of-Table/ba-p/1466130

this seems to be working ok, however am having trouble with my expression. My data consists of a table with an employee no. sick_flag, date and month.

I need a rolling 12 month count of employees who have taken an excess of 30 sick days. This is what i have so far 

count(if(aggr(sum({<MonthDiff = {"<12"}>} sick_flag), [Employee No.]) > 30, [Employee No.]))

This gives a wrong result, then when i click on the month on a visual chart, the count changes.

Just need to find a way to sum the employee sick flag for the last 12 months, and if it is greater than 30 then add to a count that is shown for the respective month on a bar chart.