That's an interesting observation. I have never looked at it quite that closely.
My experience has been that my very best results with the Apotar come at f8 and f11. I suspect that any focus error I have introduced is probably inside the circle of confusion at those apertures.
I have also had pretty good luck with portraits by actually measuring the distance from the very back edge of the accessory shoe (which I estimate to be the film plane) to the subject's nose. I've never done that with my Apotar but I have certainly done it successfully several times with the Schneider Kreuznach Radionar 4.5/105 on my Balda Baldalux 6x9. I know that isn't an Apotar but it is still a very nice triplet as well. I'm not sure I would try to do this professionally but with my grandkids it makes a great game and gets them smiling every time.