Canon lens micro focus adjustment ?

[Mike Tracy]

In response to Arthurs reply to a photo I posted the other day and my continued on / off again results I decided to finally set aside the time this morning to give it a go with the combo I mostly use. The settings I arrived at from my MKIII after being as thorough as possible are as follows.
EF 500 f4, -13
With 1.4x, +3

I might add I tried a few different ways of doing this per others recommendations on a couple of respected sites as well as my own variation and arrived at the same settings for each. Is it unusual to have such a wide swing between lenses and will these new settings produce any real world differences ? I won't be able to go in the field for a couple days to compare the before and after so I was wondering what others experiences with this produced.

Thanks.