Railing post positions can sometimes cause the base to extend beyond the width of the perimeter strip. This creates a gap the same height as the perimeter board between the decking and the base trim. A common practice is to scribe the base trim to profile around the perimeter board. However, this can pose safety issues.
To fill the gap, cut a rectangular, same-color piece off the lip of the perimeter or feature board and slide it underneath the trim collar at the base of the post. This will result in a picture-frame look with a flush profile at the bottom of the post.