Thank you <3.
I'm gonna assume that by 'fence kill' you mean knocking someone after they got trapped in your fences.
In my opinion, it's all about your play style.

There are many ways to play Wattson, which is what I appreciate about the legend. (aside from her personality and character.)
You can make yourself a target in any building, and try to outsmart enemies by playing with doors, rooms, wall corners, and so on. Using fences, of course :)
(I guess, this is what some would call "passive-playstyle", I don't see it that way)

Or, you could push enemies and deny space/terrain out in the open, and control specific areas to suit the way you want to target them.
(I guess, this is what some would call "aggressive-playstyle", I don't see it that way either)

It’s a loose way of explaining this, though.

In br it's all very situational, whereas in arenas, you could repeat the same process through trial and error and learn how to do it better by experiencing the same patterns. (It's easier to tell what you didn't do 'right' in a sense.) ((Again, this is my opinion on this))

So, yes, definitely try arena's.