Star scheme

Hi,

building my first model and I got stuck. I have Actuals fact table conected to Chart of accounts Dim through Account field. Dimension table has data organized on three levels (account, group, subgroup) and I have Calendar table apart. The problem comes when I add Forecast table that has data only on Subgroup level. How to connect it with Actuals? I tried to put it together with AC data in Excel (Account,Subgroup,Amount,date,type(AC/FC), but as my FC has only data on subgroup level filter context doesn't function for FC data. Guess the problem is M:M relation on subgroup level. Any idea/resource link how to tackle this granularity?

thanks