Long before vinyl graphics appeared, the bottom edge of the door was the accepted standard to measure from for lines of lettering. Since the bottom edge was usually somewhat parallel to the ground—though not always—measuring from the bottom of the door rendered the most pleasing visual. But sometimes not, even back in the 70s. This was true not just with lines of lettering, but when installing body side moldings, too.
In the above examples, the top line is parallel to the ground, but my eyes tell me it appears slightly lifted on the right. On the other hand, if you cover the entire bottom example with your hand, the top one seems to look fine.
If I'm running the shop, I would probably let either one go out the door, unless the client voiced an objection. They're always right, right?
If the quarter panel must have an additional line of copy, it should generally be on the same plane as the door lettering—not at an angle of its own. Or, put the secondary copy in a bouncy script and then it's a moot point.
My mentor always said, "If it looks right, it is right." Unless the client says it's wrong.
Brad in Kansas City