Your absolutley right, but its the way 14 and 10 point Ariel come through in my version of MS Paint.
Try using 7/8 for credits and 10 for the main text, you should obtain the proper text dimensions, Ive done the same on all my drawings and it worked pretty well.
The reason for the text dimension incongruence lies behind the different versions of Paint. I actually did not understood actually which versions and why, but as I said the above the text dimensions mentioned above are a good escamotage.