What do you mean by senget a bit? Doesn't the WC sit on the floor of the toilet? Or are you talking about the piping to the sewage? Sometimes, your sewage pipe outlet (known as the flange) could be too far or too near the wall. You will need to use slightly curved connecting pipes.

Does that mean syphonic WCs cannot use offset connectors?

Now you guys are making me unsure about getting syphonic WCs What I like about syphonic isn't the noise, but the fact that it doesn't splash when you flush. You could actually flush while still sitting down heh heh.