Seems that this is finally done. I recived help to resolve it using Calculated Members (my MDX skills still sucks)

Sum(Descendants([Document Type].CurrentMember,,LEAVES),

Iif([Document type].CurrentMember is [Devolution], 0,

([Measures].[Invoiced]-[Measures].[Mfg Cost])

/[Measures].[Invoiced]))

Thank you both for your time