DAX calculation of variable inside iterator SUMX

Hi guys! 

Really need your assistance.

I've been struggling with one case for more than week...

Input: 

Table 'F_ERS_SellOut' with sales transactions. 

Each row is fact of weekly sales [PostingDate] for one product [ProductCode] in specified store [StoreCode] .

My task:

I need to calculate [sales amount] of products with the price 20% lower than their regular price. 

I've stuck with regular price definition... Regular price is the max price [UnitPrice] of product in particular store for the last 70 days from "current" date [PostingDate]

My solution and thoughts (below attached code script too):

The measure always returns blank.

I realize that my mistake somewhere in calculation of Regular_price variable.

And also know that I have poor understanding of context transition inside nested iteartors so far...

I will be gratefully thankfull of brief explanation of what I'm doing wrong..

Thank everybody in advance!

Value_of_discounted_products = 
            SUMX(                     
                FILTER(F_ERS_SellOut;     
                          VAR Cur_Date = F_ERS_SellOut[PostingDate] 
                          VAR Regular_price =    
                                             MAXX (                    
                                                CALCULATETABLE (       
                                                ALL(F_ERS_SellOut[PostingDate]);
                                                DATESINPERIOD ( 'Calendar'[Date]; Cur_Date; -70;DAY) 
                                                                );                                                       
                                               F_ERS_SellOut[UnitPrice]
                                                        )
                            RETURN
                            F_ERS_SellOut[UnitPrice] <= (Regular_price*0,8)); 
                            [Value])