QuincyAbeyie
I'm not sure why you would think we are much better than them, and I disagree, playing away in Europe is considerably harder than playing a good team at home in a domestic tie. Honestly, you can count on two hands the number of times we played well away from home in 30 years.
If you assess the odds on winning away from home in European football, I bet it's significantly lower than winning at home, and given that these are two-legged affairs, it makes perfect sense to limit exposure away and maximise approach at home. Obviously, it only works if you win at home, and that hasn't always been the case for us in recent times.
If you want to look at the opposition, then Porto have been beaten at home by quite a few teams in recent years, so odds are probably higher on winning there. At the same time, our record away from home has been poor ever since we entered Europe, so the odds drop back down.