After some testing, it appears that the font size increases or decreases automatically to fit the people from your tree you ask to print. If you have just a few people (e.g. yourself, a couple of siblings, your parents and each of your grandparents), printing 1 page width x 1 page height, you'll get a reasonable size for each person's box & font. But if you choose to print 2 pages width x 2 pages height, the boxes and font will be much larger. Conversely, if you choose to also print each of your great-grandparents also, the boxes and font will shrink enough to fit the extra people.
I don't know how you would simultaneously increase the font size while also decreasing the number of pages on which your tree is printed; normally reducing the number of pages will also reduce the font size (and box size).
You may need to export your tree and then import it into another family tree application that might allow you to get the results you're wanting. But I don't think Family Echo can do it.