Hey, I have a problem:
I originally used a P1S with a 0.4 mm steel nozzle (non-hardened) and achieved perfect ironing results with a completely smooth surface using Sunlu PLA Matte.
Now I am using an H2C with a hardened 0.4 mm nozzle and also a high-flow nozzle, but no matter which settings I try, I can’t achieve the same surface quality anymore.
Does anyone have recommended parameters for this printer + filament combination?
I recommend doing a specific ironing test to find the best settings for your nozzle and filament. If you simply adopt other settings, they may not work for you. This also means that you have to perform this test for each type of filament.
Make sure you use the original creator’s print profile. Once you have completed this test, you can try more specific optimisations. This test provides the most important basis for ironing. 
Unfortunately, I do no ironing with my H2D! Whatever settings, except for small area or/and where there is no change in geometry (hole etc) I rely on my P1S.
I think not only the settings but also the fans (part and auxiliary) make a difference, may be need to play with the part fan on delay but I did not try
H2D, so certainly H2C and may be H2S are not the best with ironing. With P1S I can achieve almost injection quality, nowhere near with my H2D.
Thats such a relief to hear.
I’m driving Crazy Not Findling the Right settings.
Have you checked out the wiki yet? There are some useful tips there too.
Otherwise, for topics like this: photos, photos, and more photos. They often say more than just, “I can’t find the right settings.” 
If the system says that you can upload your photos, you have to complete the mini tutorial with the rules, which only takes a few minutes.
Testing has been the only thing that has ever helped me with ironing. That test Retro linked is good and sorts it out. Use the same roll of filament and as much of the same process settings as possible
That’s a good tip: I had to do this separately for each type of filament, as there are big differences: PLA, PLA Matte, PLA Silk… and of course separately for each manufacturer. 