Ssrs report size is changing

I would like to find a way to keep the main tablix that is an ssrs 2008 report from changing sizes.

In a new ssrs 2008 report, I am embedding several tablixes into a main tablix since all the tablixes refer to the same student. I am using the same rdl in all cases. Each embedded tablix represents report(s) the user can choice to execute.

This is working so far since the reports are showing up. The problem is every time I embed a new tablix within the main tablix, the size of the main tablix changes and all the formatting I have worked on changes. I keep embedding new reports everytime a create a new report. This process will continue until I have added 12 more reports.

Thus I know that a rectangle will keep formatting options, but I need to make certain I can keep adding embedded tablixes to the main tablix.

Thus I am wondering if I should start with a rectangle and embed the main tablix. If not, should I start with the main tablix and the embedded the rectangle and then add the embedded tablixes? If not should I have the main tablix, embedded the tablixes created so far and then add the rectangle.

Basically I would like to know what you recommend and why. I do not need to use rectangles unless you think that is a good idea.

found solution. set cangrow to true.