Help requested on Advanced DAX Problem

Hi DAXStudent ,

Here is your solution.

Steps:
1. Create a calculated column inthe transaction table

DOS-Relative Month Key = 
var Yr = year(Transactions[Date of Service])+1
var Mo = month(today())+Transactions[DOSMonthDiff]
Return
date(yr,mo,1)

2. Make an inactive relationship between the new column and calender date

3. Now Make a new Measure to use in the matrix

Payment Amount Divided by Whole Year Total - Last Year (New) = 

Var Current_Payment = CALCULATE([Payment Amount],USERELATIONSHIP('Calendar'[Date],Transactions[DOS-Relative Month Key]))
Var Total_Payment = CALCULATE([Payment Amount],ALL('Calendar'),'Calendar'[Year]=SELECTEDVALUE('Calendar'[Year])-1)

RETURN

CALCULATE(Current_Payment/Total_Payment,USERELATIONSHIP('Calendar'[Date],Transactions[DOS-Relative Month Key]))

Now make the table to get the desired result. 

Hope this will solve the purpose. If you want something more specific, let me know

Else Plz accept as solution.....