Although the Barcelona v Espanyol match is a derby match, the quality of the two teams clearly has a significant difference. Moreover, this season Barcelona is still in a trend that is very under Hansi Flick, while Espanyol is in the bottom position of the standings and very close to the relegation zone. Thus, there is no doubt for me to choose Barcelona to win at least with a score of 3-0 or maybe more. But yes, because I have high confidence in Barcelona, choosing Barcelona -2.5 or maybe -3 can be an interesting bet with good odds as well as with an Asian handicap option like that.
I think I absolutely agree with you about giving Barcelona -2.5 or -3 goals and still expect them to win against Espanyol tomorrow and that's they've not just been the most prolific team in the Spanish La Liga this season but have managed to score 21 goals in their last give games in all competitions. Camp Nou is their fortress and beating an average team like Espanyol with a high goal margin is very likely to happen tomorrow. I'll be checking out the odds and see if they'll tempting enough for to stake on this particular option you suggested.