Average on Deals Above/Below 10K

Hello there, i've built a search by customer that shows the count of Sales orders below and above 10K, and the amounts for each, i thought i'd be able to calculate the average for below and above 10K simply by using the formula CASE WHEN {amount}-NVL({taxtotal},0) < 10000 THEN {amount}-NVL({taxtotal},0) ELSE 0 END (also highlighted in search snip below) and set the summary type to Average, but appears that it's calculating the total average by dividing the correct amount by the total order count per client, and not just those with a value below 10K, is there any adjustment i can make to this formula so it just calculates the average using a count of Opps below 10K? Criteria and columns are below, would appreciate any advice, thanks for your help.