Strange Problem with Adding Text to PNG

Hi everybody!

I'm trying to add English text to an Italian comic I've scanned. I scanned the pages 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 English text to the dialogue balloons, 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 know of 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.

There has to be a simple solution to all this, but being a relative Photoshop newbie I wouldn't have a clue what it is.

Many thanks in advance to somebody who can solve this problem.

Be sure to highlight the text before making size changes.