I avoid this by manually adding new lanes if the part isn't going to overlap a previous take. That seems to make any new audio land in the new lane. It shouldn't be this way but it's not a big deal to to me to click the little plus button before recording my new part. The weird thing is sometimes a new lane will be created automatically but other times it won't. There is certainly room for improvement.
I've been meaning to try adding a bunch of empty lanes to see if new, non overlapping audio lands in the new lanes automatically but I haven't been tracking at all for over the past month or so as I study. I don't even sit in front of the DAW while studying anymore because I'm working on general mixing concepts as opposed to Sonar functionality.
Some day I'll actually make some music with all this stuff. lol