On a phone, so sorry for terse reply:
You need about 50x the focal length for test distance. So 20m for a 400mm lens (though calibrating at your most commonly used shooting distance is also probably fine too).
Focus on a target using live view or manually (MFA has no effect here; it should always be "perfect"). Set the lens to MF, IS off. Set MFA to -20 and check for the dot by half pressing the shutter button. Try -15, -10... up to +20. Narrow down on the range where it illuminates constantly (no flicker).
If you get -10 to +5 the MFA to dial in will be -2.5.
For +1 to +8 it'd be +4.5.
Obviously you can only choose whole numbers so just go for the nearest.
I tend to go up and down the MFA values a few times just to be fairly certain where the edges are of the good range.
I did what you have indicated above .....However as I said in my above post there was no dot appearing in Live view...unless I was missing it amongst the other screen icons. I will try again tomorrow with this method for 100-400 . Maybe that will work ok
BTW.... I think its important to point out that many canon users are thinking to put the camera in LV to do these tests. But if the user focuses using live view the camera is using contrast detect to focus, which to my understanding of the way my camera works entirely bypasses the phase detect autofocus system that the DSLR uses when you’re looking through the viewfinder. It is the phase detect system for which microadjustments are necessary, not the contrast detect system (which should always be accurate with a high contrast target, decent light, and camera locked down on a good tripod).
So all my tests have previously been done through the lens align method through the viewfinder using phase detect and then adjusting via MA. What I need to know is how to do this via the green dot method not using LV with camera locked in Manual Focus in Viewfinder mode. And tahst where the issue is because once the lens is in manual focus and viewfinder mode half pressing the shutter to get the AF dot happening after a MA change results in no AF light/dot flashing in viewfinder.