I respectfully suggest the coupe and convertible are different castings. There are many differences between them. It is not like they just lopped off the roof and made a convertible. It's also not like a Johnny Lightning or Greenlight engineering job where both models were designed to come off the same tool.
Here are some comparison shots:
Hood and grille lines are subtly, but clearly different. Corner radius of grille very not the same. Hood detail also different (more prounounced on coupe). Doors appear larger on the coupe.
Base is different, as is how the base attaches to the body. Different castings designed separately, in my opinion FWIW.
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