hi @guido.saccon,
servoj is targeting to be as close to the joint positions as possible, so the error is only considered at the discrete points in time. In the theory higher frequency, lower lookahead_time and higher gain will reduce that error. But will result in huge acceleration peaks.
In your case it sounds like servoc is a better choice because it will be easier to predict the speed and acceleration. So please take a look at that function. There is a little more description of the functionality here