Grand Total Not Calculating Correctly

Hello,

I am creating a P&L budget using a drilldown matrix. For Expense, I have different rules for each "Sub Expense category" eg to exclude certain Cost Centres and Activity Type Areas. To do this, I have used SELECTVALUE to know which "Sub Expense category" rule to apply.

I create a measure to calculate the 'Budget Year 1'. The totals are correct at a row level, but it calculates the total Expense wrongly as it is ignoring the "Sub Expense category" rules, and also does not calculate at a grand total level. How do I get this to work and is this possible in Power BI? I want the expense to total at every level, the total Expense (ie -7 + 49) and finally Revenue - Expense (-7+49+60) at a grand total level.

Budget Year 1 = 

var firstCategory = SELECTEDVALUE('P&L Structure'[1stCat]) 
var secondCategory = SELECTEDVALUE('P&L Structure'[2ndCat]) 
var revenue = SUMX(Budget, Budget[Amount])
var expense = 
SWITCH(TRUE(),
secondCategory = "Salary", - CALCULATE(SUMX(Budget, Budget[Amount]), FILTER(Budget, NOT (Budget[CostCentre] = 9900 && Budget[ActivityArea] = "AA1"))), 
secondCategory = "Exception Salary",  - CALCULATE(SUMX(Budget, Budget[Amount]), FILTER(Budget, NOT (Budget[CostCentre] = 9600 && Budget[ActivityArea] = "AA1"))))
var result =
SWITCH(TRUE(),
firstCategory = "Revenue", revenue,
firstCategory = "Expense", expense)
RETURN
result

Attached is my example pbix file.

https://drive.google.com/file/d/1nWPTQJglcJX7oHoBAJuJBNIjGs79AKed/view?usp=sharing