Unity Smart Merge (UnityYAMLMerge.exe): how to configure vsDiffMerge.exe in the mergespecfile.txt?

I created a proxy script as:

 o:\git\tools\vsmerge.bat

Content:

 "c:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\vsDiffMerge.exe" /m "%1" "%2" "%3" "%4" 

I am invoking this from mergefilespec.txt:

  * use "o:\git\tools\vsmerge.bat" "%r" "%l" "%b" "%d"

It did not work without the proxy script. This way though the merge button works in the team explorer from VS for code.

I found a solution that worked for me (although I could not correctly configure the mergespecfile.txt file to use vsDiffMerge.exe):

in .gitconfig I added an addition entry:

 [mergetool "vs"]
     cmd = 'C:/Program Files (x86)/Microsoft Visual Studio 12.0/Common7/IDE/vsdiffmerge.exe' $LOCAL $REMOTE $BASE $MERGED //m
     trustExitCode = true

And in the console I run:

For .prefab and .unity:

 git mergetool

For .cs:

 git mergetool --tool=vs

If I need to run for a specific file:

 git mergetool --tool=vs *<file_name>.cs

Here is my whole merge/diff configuration in the .gitconfig file:

 [mergetool "vs"]
     cmd = 'C:/Program Files (x86)/Microsoft Visual Studio 12.0/Common7/IDE/vsdiffmerge.exe' $LOCAL $REMOTE $BASE $MERGED //m
     trustExitCode = true
 
 [difftool "sourcetree"]
     cmd = 'C:/Program Files (x86)/Microsoft Visual Studio 12.0/Common7/IDE/vsdiffmerge.exe' $LOCAL $REMOTE Source Target //t
 [mergetool "sourcetree"]
     cmd = 'C:/Program Files/Unity5.5.1f1/Editor/Data/Tools/UnityYAMLMerge.exe' merge -p $BASE $REMOTE $LOCAL $MERGED
     trustExitCode = false
     keepTemporaries = true
     keepBackup = false
 
 [merge]
     tool = sourcetree
 [diff]
     tool = sourcetree
     
 [core]
     autocrlf = true

So, this solved my merge issues with the .cs files (which was my main merge configuration problem). But my fallback tool in the mergespecfile.txt is still p4merge (which does not bother me so much to solve unsolved scene and prefab conflicts the Unity Smart merge could not handle):

 unity use "C:\Program Files\Perforce\p4merge.exe" "$BASE" "$REMOTE" "$LOCAL" "$MERGED"
 prefab use "C:\Program Files\Perforce\p4merge.exe" "$BASE" "$REMOTE" "$LOCAL" "$MERGED"
 
 # Perforce merge
 * use "%programs%\Perforce\p4merge.exe" "%b" "%l" "%r" "%d"
 * use "%programs%/p4merge.app/Contents/Resources/launchp4merge" "%b" "%l" "%r" "%d"

If anyone knows how to configure the mergespecfile.txt to work with the vsDiffMerge.exe as the fallback tool I would like to see the solution.