RollupConditionalSum in IfElse Statement


our company is dealing mostly with yearly subscription customers, but some of them are on multi-year and half-year contracts.

I wanted to display the current annualized invoice revenue on the associated account record and came up with the following formula on a custom decimal field type.

However, my formula doesn't seem to be stable and displays wrong amounts for some account records.

   equal(related($members,"cover_period_c"),"Half-Year Customer"),
         equal(related($members,"cover_period_c"),"Multi-Year Customer"),



The formula is supposed to display the following for the Financial Year 2020:

Half-Year CustomerFY2020 total invoice rollup in AUD
Multi-Year Customer not expected to be invoiced this FY (Next-Renewal <> 2020)previous FY annualized invoice amount (here FY19)
1-Year Customer & MY customers being invoiced this FYFY2020 annualized invoice rollup in AUD