Answer to my own problem - I found out it had to do with my Win 10 Display being set to 150% scaling. When I set scaling in Windows display to "normal" 100%. the raw mode crosshairs behave normally and reach all corners with both guns. It seems to be a problem with Demulshooter that some other users used to have with other lightgun/emulator settings before.
Now I just have to find out how to tell demulshooter to accept my 150% scaling without issues. Taskbar text is much too tiny to read on a big tv...
EDIT: Easy Fix. I just had to set the demulshooter.exe to "application" in the High Dpi Compatibility Settings. Now it works everytime without me having to change the Windows scaling settings. I also set this for the emulator.exe / emulator_multicpu.exe just in case, maybe that's not even necessary. Ok case closed.
It's possible to make model 2 emulator work with Lichtknarre and two wiimotes and just one Mayflash Dolphin bar with custom firmware and vigem plugin.
EDIT 2: Some days later, and after taking a deeper look into my problems with newer versions of Demulshooter, I found out current versions (right now I'm testing 15.4) of DS ARE actually still working with Lichtknarre and Model 2, but there are some major issues to be aware of and some differences in how the different versions of Demulshooter have to be handled. All in all I still recommend for Model 2 on Lichtknarre vigem to use an older DS version (I used 8.7 and it's working fine as described here before).
On 15.4 Demulshooter won't show any gamepad devices but exclusively device HIDs. That is actually not a problem, as the HIDs of the vigem virtual gamepads will show up and can generally be handled just like before. The DemulShooter GUI will not present anything about mouse buttons, but offers generalized game functions like trigger, reload and so on. That's also not an "issue".
What IS an issue, though, is that Lichtknarre would lose communication with my windows game controllers setup the moment I start either the DemulShooter_GUI.exe or the DsDiag.exe. My movements are suddenly not registered anymore. This was happening all the time at first and probably why I was thinking it wasn't working at all. Now I find out I can set the right settings and HID titles in the DemulShooter GUI, then save my config and exit. And after that I have to quit and restart Lichtknarre and my wiimotes would be working again then.
But it's generally a bit unstable and I had no issues of that sort with the old 8.7 version of Demulshooter.
Another thing to keep in mind is a little thing changed in the way you have to write your bat to get the right command lines working: On 8.7, if you want to use the emulator_multicpu.exe and not the emulator.exe to run the game, you had to write in -target=model2m. This changed for 15.4, and -target=model2 will work for BOTH exes. Your bat will actually crash if you still use -target=model2m in the new version 15.4.
Then it is according to the Demulshooter wiki on github mandatory in 15.4 to install the Demulshooter model 2 crosshair scripts to see crosshairs at all and set DrawCross at 0 in the emulator.ini. It wasn't mandatory in 8.7, I used the native crosshairs with it with no problem and left the setting in the emulator.ini at DrawCross=1.
This mandatory install of the Demulshooter crosshair scripts leads to a further problem when you are using Warped Polygon's 16:9 scripts. When I installed these crosshair scripts over the Warped Polygon pre-configured scripts, everything was set to 4:3 again. If I want to use Warped Polygon's pre-config files and keep them working, I will have to stay with 8.7 and NOT install the Demulshooter crosshair scripts.
Then it's very important it is the correct way for the 8.7 Demulshooter setup to put UseRawInput to 1 in the emulator.ini of the m2 emulator. Otherwise you will simply have no second crosshair and can't play multiplayer.
In 15.4, demulshooter wants you to set UseRawInput to 0 to make it work. Quite confusing!