To find the logs, just enter %LOCALAPPDATA% into the address bar of Explorer and hit your Enter-Key, in the folder you are taken you have to scroll to its very end, there you will find Krita’s log-files. In case you can not see the file name extensions, you have to enable the view of file name extensions in the “View” menu of Explorer what you will find at the top of Explorer, it is a checkbox from those 3 checkboxes on the right end of the “View” menu.
For the start with scaling factor I’ve prepared a small batch-file, you can open and edit it with Notepad or any other editor you like, just do it with a copy of that file, so you have a backup
If you installed Krita via its installer then you don’t need to modify the path in that file, just adjust the number behind the equals sign, try to begin with de-/increments of 0.2 to see in which direction you have to go, then you can take smaller steps.
After you have found a scaling you like, you can hide it in a folder you seldom visit, maybe together with Krita’s settings in %LOCALAPPDATA%, and set a link to it, or leave it on your desktop and start Krita directly using it, or even start Krita with it out of your “Start” menu,
which @freyalupen described here in more detail.
Here you can download the batch-file:
Hoping that I’ve nothing forgotten. 
Michelist