The reported "System CA" at the outfall element is not correct and appears to be double the expected value.
This is a known issue: Defect reference number #333602.
There are two workarounds for this issue, to correct the value of system CA at the outfall; as follows.
In StormCAD (GVF-Rational Solver), how is the conduit property "System CA" computed?
System CA results for a catch basin are lower than the CA results for the upstream catchment