its very diificult to say. Everyone has got only a few informations.
I have had a level 6 myself. And I had an 8 week injury of a 21 year old. In the beginning it seemed that the doctor was able to lower one week injury in only 6 days. then a few weeks later in took him 7 days to decrease injury length 1 week. So my first assumptions were that the sublevel of my doctor had decreased. However a had 3 more 2 week inury during that time. Most of those injurys and most of them took 6 days...
next guess: my 2 weeks injurys are a little younger (20,19), so this might be the tiny bit which made the 1 day difference...???? maybe
i have heard from somebody who still has Max Payne. He told me that Max neede 10 days to cut of 1 week injury...
maybe we can collect some more data on this topic, to figure out the differences between the doctors