How to change sort/display order of Summary field in Portal

[rogerbowering]

 have built a banking application essentially containing Accounts with a link to transactions. I like to see the transactions associated to each account in Date order descending, so they show most recent transactions at the top

 

I want to see the current balance/running total beside each each transaction for which i use a Summary field,

 

In the examples shown in the image - if the transactions are sorted in Date Ascending order then the running totals are correct; but if they are sorted in Descending order (which is what I want), then the running totals are meaning less to me (even if correct to Filemaker) as the Summary total seems to start at the top and work down