When my legend includes a Greek letter, the preceding bar (or symbol) is larger, so doesn't match others on the page.

Here is a way to work around this bug (in all versions of Prism). Put a greek letter on all of the legends. That way, the size of the preceding bar or symbol will be equal.  For legends where the Greek doesn't make sense, select that Greek letter and make it white (or whatever your page background is) so it is invisible. Do this from Change... selected text. Prism will "see" the Greek and make the bar larger, but you won't see the Greek since its color matches the background.