For my use, I set up the bill about 6 inches from the end of my lens.
I ended up with +5 being noticeable sharper in picking up the clothes fibers inside the bill.
This was with a tripod and bracketed sets of 3 shots at each MFA step.
The AF was consistently sharper at +5
I retested the lens on a few item, such as a soda bottle label at 3-4 feet and the lens was no less sharp with MFA +5
The AF and MFA will behave differently when comparing macro distances to infinity. But I am happy with my adjustments.
I have have to remember to set my ISO shutter speed to 1/125 even with the IS. But that's only an issue in natural low light.