Sorry, what you are looking for is not currently supported. At least not in real-time.
Actually, I did not even know that "legato" (which is usually referring to pitch) extended to clip playback position in Ableton.
Just to be sure that I understand you, and how this feature could work...
Imagine that we have two phrases, one with 32 lines and one with 48 lines.
Also, Redux is set to mono trigger option (legato mode).
Example #1: we trigger the first phrase, and then shortly after, the second one.
- From what you describe, I would expect the playhead to move to line 33 of the second phrase. Or?
Example #2: we've triggered the second phrase, and shortly after, the first one.
- Now I would expect the playhead to move to line 17 of the second phrase, because 48 "overshoots" the 32-line by 16 lines.
Did I get this right?