Incorrect watts vs. resistance on Tacx Ironman Smart trainer

I just set up my smart trainer, but Zwift in-game resistance / speed vs. watts doesnt add up at all. I also have a “proper” ergometer at home, so I roughly know how X watts feel (and where my FTP is situated). These ergometer readings also translate quite well into the speed I am getting on the road with the road bike I am now using with my Tacx; so it’s not the setup / bike. I am using a Tacx trainer tire, and I can rule out errors such as the breaks rubbing against the rim.

I tried the trainer difficulty setting, to no avail (that doesn’t even seem to do anything).
I double checked my physical data, it’s correct.

What else can I do actually make riding in Zwift realistic? Is there any “calibration” ride or something like that I overlooked? Or do I actually have to do something within the Tacx trainer software?

Thanks a lot for any suggestions!

You should get the Tacx Utility app (iphone and Android) and calibrate your trainer. It’ll also tell you if the roller is too tight / loose.