Than this issue is solved.
@Linui this could be interesting for you, too.
Recap:
Linear advance, Junction deviation, accelleration, flow and speed really made visible differences. But the real problem was created by the cura feature compensate wall overlaps.
I found a few articles that such problems can be caused by this feature - our printer is no ultimaker, so features for this printer doesn’t necessarily have to be suitable for the snapmaker.
It’s enabled by default, so deactivating it might be a good idea.
On the other side, if the compensation algorithm is good for snapmaker, too, it could be possible that I still have a flow issue. But this is influenced by material, nozzle, line width, e-steps and so on 
So, the possibilitys are endless.
Just keep in mind that a feature like this exists in the cura configuration.
Thanks at all!
