Electrically small antenna CST versus HFSS

[KP18]

I am a new user to CST and I am trying to figure out if my setup is correct with correct parameter settings. I am simulating a very electrically small antenna with a waveguide port. I have sent the model to my CST application engineer and he is telling me my results are correct however I keep running into a warning "Total Efficiency is smller than 1e-4 Farfield innacurate!". I need to get an accurate farfield so that I can determine if my antenna gain will be in the correct direction for the specified application. Does anyone know how to work around this error or is there something in my setup that could be incorrect? I am using the transient solver with the accuracy setting at -50 dB, subgrid meshing, and open boundary with added space of 4. (The help file does not define this surrounding space very well either what are the units or is it mesh cells what is the typical rule of thumb for CST?)

Also, would HFSS do a better job at modelling this. Is this a solver assumption in CST?