Don't pay attention to the Burwell link. It's for guns that don't have the Apex parts in them.
Look at this pic:
The red arrow is pointing to the place you'll need to smooth out. Once you take the slide off the gun and look at this surface, you'll see exactly where the polishing needs to be done.
With proper trigger technique you'll never notice the "gritty" feel, but it's your gun so, polish away.