Hi Tim,
To be honest, I do not use the Gantt Chart area in Portfolios as I too need different groupings to categorize the projects. I have a report* that lists the projects the way I want and then I use the new Gantt Chart icon in the upper right hand corner. However, there is one issue with this and that is you cannot export the new Gantt Chart functionality so we do have to do screen grabs to capture that view.
*- You can also use a combination of custom view and grouping to get the same result in the Portfolio area without doing a separate report, if you'd like.