QSOs are much easier as they tend to be very repetitive. Just drill the abbreviations, Q-codes and prosigns.
Hmm... I am now doing 18wpm/18wpm random 5-letter groups with more than 90% correct for every try, but I still struggle with on-the-air QSO's...!!
I wonder why that is then... Maybe I haven't been exercising enough abbrevs, prosigns and Q-codes, although I have been doing those for some time now. Maybe it's because QSO's on-air are faster than 18wpm, and when they're not, they are much slower, and hard to copy because you can't recognize slow code as easy in head. Maybe it's because there is QSB, fading, QRM, bad fists and bad code, I don't know... Maybe it's the psychological factor, that you are not listening to a computer, but instead, a real person. All I can say, is that for me, QSO's, are still after little more than a year, very difficult to understand... And I'm still doing random strings of 5 at 18/18, and listening to up-to 5-letter english words in my car, at 23/23.