I like the movement engine. It doesn't quite have the feel of N at this stage, but it does feel awesome.
I used the following conditions:
- LOS to make sure there's no wall in the way
- X check to make sure the player is horizontally close to the thwump
- Y check to make sure the player is below the thwump.
It's been a while since I've played N, but I think this behaves the right way. (Obviously it doesn't go back up - but I'll leave that one for you!)
By the way, your LOS behaviour had some strange settings - with sensitivity like that, I don't think it would ever find anything. Also, the thwump itself was set to 'solid', but the LOS was blocked by solid objects, so it was effectively blind.
I find it's often worth making sure something works by itself (like the LOS check) before trying to get it to do what you want!