SSRS expression help request: How to sum DISTINCT records only in the numertor of a division?

=SUM(SUM(IIF(Fields!MannerofDisputeResolution.Value = "Claim Struck Out",1,0))+SUM(IIF(Fields!MannerofDisputeResolution.Value = "Won at Trial",1,0))+SUM(IIF(Fields!MannerofDisputeResolution.Value = "Discontinued",1,0))) /COUNTDISTINCT(Fields!Reference.Value, "FraudType4")

Hi everyone

I'd like some help with an expression, please?

Can anyone advise how I only sum the distinct reference numbers that fall into the MannerofDisputeResolution (the numerator) so they are distinct like in the domoninator?

Thanks!