Photoshop :: Adding Text To PNG

I'm trying to add text to some PNG images. I scanned the images at 600 DPI, saved them as PNGs, then reduced the size of the images to 19 percent of the original scans. The problem is when I try to add text to the images, the text remains the same size as it was in the full-size image, even though I've set the character size to 8 points in the character options box. The only way I've found to get around this is to add the text to the full-size image, which is a cumbersome, time-consuming process, or reduce the character size to something like 1.5 points, which produces roughly the text size I'm after.