You'd need to use a script to capture and store the summary values into individual fields/records so that your portal displays a number field instead of a summary field that calculates "on display" on your layout. This also requires careful thought to make sure that any changes to your data result in your script running to update the data.
What you show is nearly identical to a set up I've used for years (originally set up in FileMaker 3). In the case where I did this, the data is not modified after close of business of the day the record was originally created so I could use a script that runs every evening to generate the summarized data in a table used for the grid of one row portals used on such a layout. The original records that are the source of this data represent over a million records so calculating the totals (and averages in the case of my report), greatly reduces the number of calculations needed and the report pops up nearly instantly.
You won't be able to open a popover "on hover" unless there is a plug in that adds that capability, but mouse click can open your popover or you might use a tool tip to show such data.