Well, just in case anyone else is stuck with the same problem and comes across this old string: After several tests I have come up with this solution that works for me - and perhaps for others too:
Notice that the subtitle borders are set differently than the default settings. The settings I use keeps the subtitle string just inside the outer safe area border where as the default settings are inside the inner safe area border and thus resulting in shorter subtitle lines.
You can choose a different typeface if you like. The typeface doesn't seem to have any influence on the "_too complex_" matter.
With these settings I can writea maximum of60characters, including spaces, per line. Remember to makeforcedline breaksbetween the lines,ifyoursubtitle stringislonger than one line.