I focus like that when I do studio portraits. Set the 90 mm to 5 feet and move in until the catch lights in the near eye merge.
Always focus portraits on the subjects eyes. Set the lens to say 8 feet, compose, put the RF patch on the eyes and focus closer until the image merges, recompose, and you take the pic when ready.
With a handy straight line in the composition, focus until the line is continuous above, below, and through the RF patch. Practice on a door frame. The shirt collar is a good target in this pic. Just use something in the same distance plane as the eye.
If the line is horizontal, rotate the camera, focus, rotate horizontal again, recompose.
If you have a lens with the pull out shade, it is as effective as the vented shades if you look at the front element from an angle. It just looks like it would not be as good.