'filter_expression:' is not supported for measures of non-aggregate type 'number'

I have a Custom Measure based on a measure type numbers that’s a division of this kind:

${TABLE}.sessions / ${TABLE}.days_in_month

Now, in one particular look I want to only get this measure based on a specific day of the week so I’m using the aforementioned measure + following filter: ${date_day_of_week_index} = 1

Somehow I’m getting an error that number is not supported for filters… Any reason why is that?

I already have an idea on a workaround (pivot by day of week + table calculations) but this would be much easier, wouldn’t it?