I have one like this that has the same problem on the side except on mine where the wood has cracked it has shrunk close to 1/4" so the wood connected at the top is even but from the split beyond, it drops off the entire length of the top. So how or what would you do to make it not as noticeable?
I had a problem similar to with with a speaker cabinet build I did a few years ago. I was using Baltic Birch plywood and one of my cuts was off by a very small fraction. I was able to cut a very thin "shim" with my table saw - just a thin strip and drop it down into the gap. A little glue on each side and it was a perfect fit. I would think the same technique might work here. Use a thin piece of wood or veneer and just cut a narrow strip and glue it in place. Make sure it is a bit "thicker" than it needs to be so it can be sanded down so it is level and smooth.
I have a box of ancient artist oil paints from my grandfather, and I myself am an antique, which even when just about dried out can come back to life with a couple of drops of unleaded, and fill in where needed or to augment a really rough project where rattle cans don't finish up properly. Don't do enough to fire up the compressor and deal with charging and then cleaning the sprayers like the old days when I'd wait until I had a driveway full of stuff to do. Anyway this is outdoors stuff only!