Outro usuário resolveu o problema:
After the excellent advice you got from @DavidPostill[,] you can now see that the red letters have a paragraph mark ("pi" sign) after them. You may have pressed Enter after typing the letter or copied the text from another source with a paragraph break. In any case, Word is vertically centering your text, but the text consist of two paragraphs so it's simply taller. Remove the paragraph mark as DavidPostill suggested and you'll get the result you want.