using a variable within a CASE statement

Hi there,
I have a fairly simple CASE statement.
In this query I derive at my commission value based on calculated values from tblCommissionTiers .
The query works well for the tiers below 100%. I'm now trying to use a variable @MaxComm to pass the highest CommissionPercentage to the same calculation as the lower values for instances when Target is exceeded.
in other words, whenever gross is more than targ.SalesTarget, I would like to dynamically apply the highest CommissionPercentage.
Can anyone assist me with using paramtres inside a CASE statement please?

here is my script

DECLARE @MaxComm decimal (3,2)
SET @MaxComm = ( select max(CommissionPercentage) from tblCommissionTiers)

SELECT DISTINCT empNum, gross as SALES ,targ.SalesTarget AS TARGET
				, lowPercentage,highPercentage, CommissionPercentage
				,gross*lowPercentage AS LowAmount
				,gross*highPercentage AS HighAmount
				,(gross*highPercentage) - (gross*lowPercentage) VarHighVsLow
				,CASE WHEN gross > targ.SalesTarget
						THEN ((gross*highPercentage) - (gross*lowPercentage)) * CommissionPercentage
					  WHEN (gross - targ.SalesTarget) > 100.00
						THEN (gross - targ.SalesTarget) * @MaxComm
					ELSE 0   END COMMISSION
FROM tblRevenues rev
  INNER JOIN tblCommissionTiers com 
	ON rev.commissionFlag = com.commissionFlag 
	 INNER JOIN [dbo].[tblTargets] Targ
	  ON com.commissionFlag  = targ.commissionFlag
GROUP BY empNum, gross,targ.SalesTarget , lowPercentage ,highPercentage, CommissionPercentage

Select allOpen in new window

My concern is the zero output in the COMMISSION column

here are my output values