Please describe this in more detail unless I've guessed correctly here:
"However when I sub-summary by one of the fields within the portal, it uses the info in the last portal record (the first version recorded for that scene.)"
I guessing that you have placed either a field from the portals table directly in the sub-summary part or you have a calculation field that refers to this field in its calculation.
If either of these two possiblities are the case here, then the problem is that a sort order specified on the portal has nothing to do with which out of many related records will be referenced. That is determined by which record is first in the relationship. You can specify a sort order in the relationship (Manage | Database | relationships, double click the relationship line) or in a calculation, you can use the Last () function to get the most recently created related record. (The most recently created related record will be the last record as long as no sort order is specified for the relationship.)
Genius! Thanks Phil! Yes, I did place a field from the portals table directly in the sub-summary part. I will adjust per your suggestions below.
You could also use a sorted, one row portal for this field.