Using Spot AF question

I don't know if this belongs here or on the MK IV thread or the 500mm thread.
If C.FNIII-6 is set to #7, Spot AF, does this actually make an appreciable difference? The active focus point blinks in my view finder but the change in actual size of the active focus point does not seem to get smaller. I may be expecting too much of a size change or it may not be working properly.
Thanks for any advice.
Ed

In spot focusing, the manual says "...the active AF point will blink brighter than usual". My guess is you're thinking the size of the red box in the viewfinder will change, and that's not the case. That box has never represented the actual area of the sensor being used to focus, it is just a pointer to give you a general idea where you are requesting focus.

Dave

Thanks for responding. I indeed did think that it would decrease in size.
Ed