[Plugin: NextGEN Gallery] Show full sized image for album preview instead of thumbnail?

I’m working on a template for a site, and the setup I’m trying to work on is as follows:

When you click the portfolio page, you will get an album preview, showing images at 356 x 356 pixels. When you click one of those images, you will get a page of gallery thumbnails displayed at 150 x 150 pixels. When you click those thumbnails, you’ll get the full-sized 356×356 pixels image.

Currently, both come out the same size, depending on what I set the thumbnail size to under the NextGen options.

Do I need to change some code in nggfunctions.php or in the album-extend.php to get the album preview to show the full-sized image, instead of a thumbnail?