Is it me but could it be that plucking with the thumb gives the overall playing a more consistent tone and even a tighter tempo than when using the usual suspects (index and middle fingers)? I was recording the same part, the same notes, in separate tracks first with the thumb and then with the other 2 and comparing the overall results and realize that the consistency was almost rivaling the quantized version of a virtual P bass which I also recorded on a separate track for comparison's sake. I'm talking about Garageband iOS version. Of course, certain basslines aren't suited for thumb plucking as may require faster notes, which the thumb can't deliver but sometimes for more simple parts, the thumb seems to be the right tool. Anybody experienced something similar?