set analysis help

[#1]

I have the expression as

=count({$<Delay_Month_Convert={">=$(=Timestamp(MonthStart(AddMonths(Today(), -6)), 'DD/MM/YYYY h:mm:ss[.fff] TT'))<$(=Timestamp(MonthStart(Today()), 'DD/MM/YYYY h:mm:ss[.fff] TT'))"}>}distinct External_HU)/ HU_Count

what I am trying to get is a %age of delayed units/ total units loaded

So my second part of my expression should have a set analysis as (Delay_month_convert = Load_month) then use Hu_count for division