Mixing Iterative with Non Iterative Functions

Hey,

I have a formula which calculates, at a customer by customer level, the value of their business if new. I need to use a sumx for this to iterate down the customer table in order to check if it is a new customer within the date period selected.

Wins (Current Year) = 
var Comp1Sel = SELECTEDVALUE('Measure Select'[Measure Select])
var Comp2Sel = SELECTEDVALUE('Measure Select (Second Table)'[Measure Select]) 
var mindate = STARTOFYEAR('Date Mapping'[Month])
var maxdate = ENDOFYEAR('Date Mapping'[Month])
return

if(Comp1Sel="Prior Year",

sumx('BU Master Data',CALCULATE([Comparator 2],'BU Master Data'[Open Month (No Blanks)]>=mindate,'BU Master Data'[Open Month (No Blanks)]<=maxdate) - 
                      CALCULATE([Comparator 1],'BU Master Data'[Open Month (No Blanks)]>=mindate,'BU Master Data'[Open Month (No Blanks)]<=maxdate))

,

sumx('BU Master Data',if(CALCULATE([Comparator 1 Exists?],'BU Master Data'[Open Month (No Blanks)]>=mindate,'BU Master Data'[Open Month (No Blanks)]<=maxdate)=0,
                         CALCULATE([Comparator 2],'BU Master Data'[Open Month (No Blanks)]>=mindate,'BU Master Data'[Open Month (No Blanks)]<=maxdate),0))
                        
)
-CALCULATE([Comparator 1],'BU Master Data'[BU Parent Group]="Unknown Wins")

I also have multiple other efficiency formulas. These cannot be a SUMX as the total by each customer will not tie to the total across the business due to blended rates. 

F&B Efficiency = 'Non Core Measures: Walk & Efficiencies'[Comparator 2 Revenue (Efficiency)]*(([Comparator GP % (Efficiency)]-[Comparator 2 GP % (Efficiency)]))

I need to subtract the new business formula from my efficiency formulas, as I do not want new business included within those rates. Is this possible given one is iterative and one is not? I cannot flag if a customer is new business as a column, as it'll be based on a users selection from the date table, so needs to be dynamic.

Any help would be really appreciated