For that 3 digit number, the last 2 digits are something like $int(fontsize in menu * 4/3), so when you set your font to 8pt, 8*4/3 is 10+fraction, so it shows 410. There's a dropdown in the font dialog for a reason, and that's to prevent what you're trying to do - set windows to use invalid font sizes. The next available font size was 10, so the last 2 digits of the 3 digit number is 10 * 4/3 = 13+fraction, so it shows as 413. When you set to an in-between number, you're setting it to an illegal size, so windows has a default size and/or font it uses instead.

If you don't like the size of the font, your choices are to either switch to a different size within that same font, or switch to a different font that either has a different appearance at the same size, or offers more sizes. So if you're using Fixedsys which has only the 9pt size available, you'll need to switch to a different fixed-width font that has more sizes available. As you test other fonts, you'll find that there can be 3 different fonts which each have a 12pt size, and they each can have wildly different ideas of how many letters can fit on the same length window line.

So it boils down to the advice I gave last time, play around with your choices until you get a font/fontsize you like. Sometimes the choice might be a font where you enabled the bold setting instead of regular, and the bold may not be obnoxious in some fonts, and when you have bold enabled, someone using the bold code has the effect of toggling the bold off for that text.