HFSS v10 had a lot better Port Field Display than v11 has. Version 10 had dense vector-based field plot, while version 11 has coarse arrow-type field plot which is too coarse and field distribution is not clear.
You can change the display scale for better display. And HFSS V11 has better accuracy for port solver. As you know, it often happens that the impedence of open transmission line is wrong, for example, I often get the impedance of over 60 ohm for 50 ohm microstrip line.