How to use Total<> over a Calculated Dimension?

[#1]

My calculated Dimension is say:

if( delivery_days > 6, delivery_date, '6+')

which I have renamed as say #Delivery

but when in an expression I write:

count( Distinct Order_id ) / count ( Distinct total<#Delivery> Order_id)

or

count( Distinct Order_id ) / count ( Distinct total<if( delivery_days > 6, delivery_date, '6+')> Order_id)

I just Don't get the result