I like those graphics, and would NOT abandon the idea for the 1/2" stripe. They remind me of the muscle car era Mopar strobe stripes, and your design lends itself very well to the shape of the car (not an easy task - job well done). However, the matte black is such a stark contrast to the other colors on the car, it seems out of place and I think that's what's keeping it from working. If the graphics were done in a color that were a variant of one of the other key colors, it would work better for me. Maybe not quite as subtle as ghost flames, but not another color entirely like black. Finally - I'm not sure what kind of vinyl you used, but the matte finish makes me think it's a calendered vinyl. Consider using a cast vinyl. Most cast vinyls have a more shiny finish, which will blend in better with the gloss of your paint. From 5 feet away, it's hard to tell cast vinyl isn't actually paint. It's harder to work with than calendered, but the results are worth it...and it lasts longer.
