Issues have a formula calculation to compute a value based on the content of notes and other attributes. The result is returned as Numeric and is the formula attribute ObjMin in the screenshot below.
Issues are GROUPed according to another formula.
I wish to calculate for each group, the sum of all the ObjMin values in each issue.
My research and attempts have resulted in trying formulae like:

However this does not produce a sum at the parent/group level.
Your advice would be appreciated. Thank you